BOSTON — Bay Staters struggling to afford hefty energy bills this winter could soon see modest relief, after state regulators instructed utility companies to slash costs.

Department of Public Utilities commissioners told the state’s six gas companies in a letter Thursday to reduce energy bills by at least 5% for the rest of the “peak season” this March and April. DPU said it cannot order the utility companies to reduce February bills to residential customers.

“The combination of increased supply costs, the recovery of unusually high programmatic costs through delivery charges, and a cold winter has driven customer bills to unsustainable levels,” DPU commissioners wrote. “These circumstances warrant immediate measures to provide relief to consumers.”

Utility companies must file their proposals to reduce energy bills by 5 p.m. Monday, with the changes slated to take effect March 1. A 5% reduction on a monthly bill of $300 would represent savings of $15.

DPU’s directive comes after mounting outcry from residents, Gov. Maura Healey and 80 lawmakers, who called on the agency to rein in costs after regulators approved natural gas rate hikes in the fall.

Lawmakers said customers faced a 27% hike this heating season, creating a major strain on residents living in affordable housing developments, as well as seniors and retirees. Eversource attributed the spike in energy bills to colder temperatures between December and January, with the increased usage of natural gas translating into higher costs.

DPU also ordered the gas companies “to accelerate efforts to promote budget billing programs for residential customers, which allow customers to spread their total energy costs evenly over time.” DPU is also considering longer-term changes to make energy bills more affordable, as companies now figure out how to restructure their expenses.

“Any deferred costs will be collected through the local distribution adjustment factor during the off-peak season (i.e., May through October 2025),” commissioners wrote. “Going forward, the Department intends to investigate whether to shift certain delivery costs from the peak period to the shoulder and summer seasons on a permanent basis.”