From left, Sen. Michael Rodrigues, House Speaker Ronald Mariano, Rep. Aaron Michlewitz and Senate President Karen Spilka talk about a compromise tax relief bill in the Senate Reading Room shortly after it was filed on Tuesday.
From left, Sen. Michael Rodrigues, House Speaker Ronald Mariano, Rep. Aaron Michlewitz and Senate President Karen Spilka talk about a compromise tax relief bill in the Senate Reading Room shortly after it was filed on Tuesday. Credit: STATE HOUSE NEWS SERVICE

BOSTON — Senators overwhelmingly approved the long-awaited tax relief and reform agreement Thursday, and Democrats then turned back a Republican attempt to amend it before shipping it to Gov. Maura Healey’s desk.

The Senate accepted the conference report on a 38-1 vote with Sen. Jamie Eldridge of Marlborough casting the lone vote of dissent. President Karen Spilka of Ashland voted “yes,” which can sometimes be an emphatic sign of support from the chamber’s leader, who often does not cast votes.

The House approved of the package 155-1 on Wednesday and kept its informal session open Thursday so that it could take its final enactment vote, ensuring that the bill could reach the governor’s desk by the afternoon.

Senate Democrats then rebuffed a Republican attempt to suspend a joint rule and amend the conference report before the last vote necessary to enact it. The bill was enacted and put en route to Healey at 1:30 p.m.

The roughly $1 billion tax bill is among the most significant pieces of legislation to reach Healey since she took office in January. The Democrat has been prodding lawmakers to finish their nearly-two-year tax talks since she was a candidate for governor.

A six-member conference committee filed its accord (H 4104) at 2:32 p.m. on Tuesday. The package’s largest item, worth about $165 million this year and up to $307 million once fully implemented, is an overhauled child and dependent tax credit.

In an attempt to relieve some of the pressure on individual taxpayers, the package would more than double the state’s child and dependent tax credit. That credit would increase from $180 to $310 in fiscal year 2023, then again to $440 in fiscal years 2024 and beyond. More than 565,000 Massachusetts families would qualify for the credit, according to a bill summary.

Other family-focused pieces of the final package revive measures both branches initially approved last year, before lawmakers retreated from targeted tax relief after realizing state tax collections had surged so high that the state owed nearly $3 billion in automatic taxpayer rebates.

The bill would increase the earned income tax credit that supports lower-income families from 30% to 40% of the federal credit, double and index to inflation the maximum senior circuit breaker tax credit, and increase the cap on the rental deduction from $3,000 to $4,000, according to the summary.

The bill would also provide a uniform estate tax credit of $99,600, which would effectively double the threshold at which the levy kicks in from $1 million to $2 million. Supporters have said the existing trigger is among the lowest in the country, making Massachusetts an outlier.

That change would cost the state $128 million in FY24 and $213 million by FY27, according to the summary.

The accord would also slash the tax rate on short-term capital gains, which stem from the sale of assets held for a year or less, from 12% to 8.5%. Democrats had been divided on how to approach that change, with the House originally supporting an eventual reduction to 5% and the Senate preferring not to touch the 12% rate.

A cost breakdown estimated the short-term capital gains tax cut will carry a total price tag of $42 million in FY24 and $49 million in FY27.

Another change aimed at businesses would overhaul how Massachusetts calculates taxes owed by multistate companies. Currently, the apportionment system factors in property, payroll and sales, and the bill would replace that with a simplified version that uses only a company’s sales. Supporters have suggested the update would encourage more companies to base their headquarters in Massachusetts.

While they move to reduce the tax burden many residents and businesses face, Democrats will also embark on a potentially controversial effort to reshape a pair of voter-approved tax laws.

The conference committee accord would change Chapter 62F, the 1986 initiative petition law that caps the amount of tax revenue state government can collect each year and requires taxpayers to be reimbursed for any overage.

Under the current iteration of the law, Massachusetts must return excess tax revenue in proportion to what each taxpayer paid. Last year, when Beacon Hill owed nearly $3 billion back to residents, the highest-earning residents got rebate checks for thousands or tens of thousands of dollars and lower-earning taxpayers received a few hundred dollars or less.

The bill would replace the proportional system with an equal payment for every single taxpayer if Chapter 62F were triggered again, regardless of how much they paid in taxes that year.

It would also require married taxpayers who file a joint return with the federal government to file a joint return at the state level as well.

Lawmakers and their allies who backed the new 4% surtax on personal income above $1 million, which voters approved in November, have warned that married couples who together earn more than $1 million could avoid triggering the surtax by filing individual returns. The Massachusetts Budget and Policy Center estimated that high-income households using that maneuver could cut the state’s annual surtax revenue between $200 million and $600 million.

The bill summary said the joint-filing requirement would be “subject to exemptions or adjustments promulgated by the Department of Revenue.”

Other changes in the compromise bill aim to incentivize new housing production by expanding the Housing Development Incentive Program, which would rise from $10 million to $57 million in the first year and then settle at $30 million annually thereafter, and increasing the annual authorization for the low-income housing tax credit from $40 million to $60 million.