BOSTON — While voters may have the final say, top House and Senate Democrats said a new decision from Attorney General Andrea Campbell reinforces their opinion that the state auditor lacks the “statutory or constitutional authority to audit any other separate branch of government,” such as the Legislature.

Legislative leaders have resisted Auditor Diana DiZoglio’s efforts to audit their operations, a bid she tried to launch in March. On Friday morning, Campbell released a letter to DiZoglio, who clashed with top Democrats when she served in both the House and Senate, in which she concluded that the auditor’s office “does not currently have the legal authority to audit the Legislature without the Legislature’s consent.”

“I believe transparency is a cornerstone of good government, but that transparency must be achieved through methods that are consistent with the law,” Campbell said in a statement.

“As the chief law officer of the Commonwealth, it is my office’s role to determine the legal position of the state by looking at the law as it exists on the books today, and evaluating what that law allows, and what it does not. After a thorough review of the statutory text, pertinent Supreme Judicial Court decisions, and relevant history, we have concluded that current law does not allow an audit of the Legislature over its objection.”

DiZoglio said she was grateful for the work Campbell and her office put into the matter, but that she “strongly disagree[s]” with the decision. And she pledged to continue her legislative inquest.

“I respect the AG’s right to her opinion, and to defend the position of legislative leaders. However, a question of statutory interpretation on a matter of such importance to taxpayers is best answered by the courts, not the executive department of government,” DiZoglio, who was not immediately available to answer follow-up questions, tweeted Friday morning. “Massachusetts has one of the most opaque legislatures in the nation and this decision reinforces the status quo that benefits powerful insiders while leaving working people in dark. My office will continue to conduct its audit of the Legislature.”

In July, the first-year auditor sought Campbell’s support for a potential lawsuit designed to clear the way for a legislative audit, but in the new letter the attorney general’s office also said its research found it is “sufficiently clear that litigation on this question is not necessary or appropriate.”

The 17-page letter from Campbell ratchets up the stakes for an initiative petition DiZoglio and her supporters have been pursuing, which would make explicit in state law the auditor’s ability to probe the Legislature. Campbell in early September certified that proposal as ballot-eligible under the state constitution, and the campaign continues to collect signatures required to advance it toward the 2024 ballot.

With DiZoglio’s initial route now appearing closed, the ballot question looms as perhaps the only option remaining for the auditor to fulfill a campaign promise and subject her former colleagues to new scrutiny. But that, too, faces new questions: Campbell said in her opinion that if the measure passes, her office might need to consider potential “constitutional” implications.

“Should the initiative become law, we may need to consider whether, and the extent to which, constitutional limitations affect how the law would apply,” the attorney general wrote.

Before Campbell certified the petition, Senate Counsel James DiTullio, on behalf of the entire Senate, urged Campbell to scuttle DiZoglio’s potential ballot question, contending it should have instead been filed “in the form of a constitutional amendment” rather than a proposal for a new statute, because the language “attempts to fundamentally recast two constitutional principles.”

House Speaker Ron Mariano and Senate President Karen Spilka quickly circulated excerpts from Campbell’s newly released letter and celebrated its findings Friday morning.

“The Attorney General’s decision has reinforced our long-held position that the Auditor does not have the statutory or constitutional authority to audit any other separate branch of government,” they said in a joint statement. “We are grateful to see the Attorney General’s legal process conclude, and we remain committed to continuing the work of the people of Massachusetts.”

The auditor has asserted that her office should already have the legal power to audit the Legislature.

State law allows the auditor to examine “accounts, programs, activities and functions directly related to the aforementioned accounts of all departments, offices, commissions, institutions and activities of the commonwealth, including those of districts and authorities created by the general court and including those of the income tax division of the department of revenue.” DiZoglio said the word “departments” in that language effectively includes the Legislature, which is not explicitly mentioned.

But Campbell disagreed. She pointed to several Supreme Judicial Court rulings that found the word “department” in other statutes does not apply to the House and Senate, including a 1978 case involving the Legislature’s exemption from the state’s public records law.

The word “departments,” Campbell wrote, was not added to that section of state law until 1920, and margin notes from the era refer to a 1919 law reorganizing the massive executive branch into various departments.

She also said other sections of the auditor’s governing statute — including the same section DiZoglio cited — refer to the Legislature as the “general court,” an indication that lawmakers never intended “departments” to apply to them.

“The Legislature would not use the term ‘department’ to subject itself to the Auditor’s mandatory audit requirement where it used a different, more specific term (’general court’) to refer to itself in the very same sentence and elsewhere in the chapter,” Campbell said.

Appearing alongside tomes of historical records when she announced her appeal to Campbell, DiZoglio said the Legislature had been audited by the auditor’s office at least 113 times since 1850.

The attorney general concluded that those past audits “do not provide support for the authority the [state auditor’s office] now seeks.”

Seventy-four of the audits were effectively summaries of state finances before 1923, at which point lawmakers transferred “the bulk” of the auditor’s financial reporting responsibilities to the newly created comptroller’s office, Campbell said. Audits after 1923 were “irregular, limited in scope, and did not examine core legislative functions.”

“Despite the existence of numerous [state auditor’s office] reports on certain discrete activities or entities within the legislative branch, we have found no historical precedent at all for the type of audit the SAO seeks to conduct now: a sweeping audit of the Legislature over its objection, which would include review of many of its core legislative functions, namely, active and pending legislation, the process for appointing committees, the adoption and suspension of House and Senate rules, and the policies and procedures of the legislative bodies,” Campbell wrote.

In an email to senators Friday morning, Spilka wrote, “I am heartened that the Attorney General and her highly experienced legal team reached this conclusion — the position we have argued for months — based on the law, the facts, and the historical record. The Attorney General’s findings are crystal clear: the Auditor’s proposed audit has no basis in law and shall not proceed.”

The News Service in September obtained and reported on the letter from Senate Counsel DiTullio on behalf of the Senate, arguing that Campbell should not certify as ballot-eligible the initiative petition governing the state auditor’s ability to audit the Legislature.

In DiTullio’s letter to the attorney general’s office, he wrote in August that he planned to submit a second letter with a response to the “broader question” of the auditor’s ability to probe the Legislature.

Spilka’s office in recent weeks refused to make a copy of that correspondence available. Campbell’s office also declined to release the letter, telling the News Service on Oct. 12 that it was “exempt from disclosure at this time due to the recognized privilege between an attorney and prospective client” and that it was also exempt under a state law that defines certain “inter-agency or intra-agency memoranda or letters relating to policy positions being developed by the agency” as exempt under the definition of “public records.”

Spilka’s office on Friday finally released the second DiTullio letter, which was dated Sept. 22 and totals 14 pages.

“The question of the Auditor’s authority to conduct an audit of the General Court is complex and not subject to assumptions,” DiTullio wrote. “Nevertheless, the law and history around this question resoundingly support the position that the Auditor has no authority to launch an unprecedented and constitutionally problematic audit of the General Court that runs roughshod over separation of powers principles.”

Legislative leaders already bring in outside auditors to look at their operations, but DiZoglio has a much more expansive audit in mind and her effort to push the auditing powers question to the ballot has been fueled by people across the political spectrum who believe that the Legislature is too opaque.