Federal tax reform may soon generate a $56 million windfall for Eversource electric ratepayers in Massachusetts.

Eversource disclosed in a filing with the Department of Public Utilities today that the reduction in federal corporate tax rates from 35 percent to 21 percent will allow the company to reverse the rate increase approved for NSTAR customers in November and to reduce the amount of increase for customers of Western Massachusetts Electric Company.

NSTAR customers will now see a $35.4 million decrease in base rates instead of a $12.2 million increase. Western Massachusetts Electric customers will see their rate increase shrink from $24.8 million to $16.5 million.

Eversource indicated that it may seek additional rate reductions next January after calculating excess deferred taxes.

“Great news for Massachusetts employers struggling to manage the high cost of electricity,” said John Regan, Executive Vice President of Government Affairs for Associated Industries of Massachusetts.

“Tax reform created a tremendous opportunity to provide rate relief to customers and Eversource deserves credit for moving rapidly to realize that opportunity.”

Attorney General Maura Healey filed a motion with the DPU on December 20 seeking larger rate reductions. Eversource says its agrees with the need to reduce rates, but calculates the numbers differently. Utility regulators will now determine the final figures to be implemented on February 1.

AIM urges the DPU to approve the rate reductions for Eversource and to review the rates of other utilities in the wake of the changes in federal tax law.