BOSTON — The Legislature this week agreed to use nearly $500 million in surtax revenue to deliver a major boost to K-12 school funding, a move that some see as fulfilling the voter-approved mission of the tax on high earners while others warn it strays from the original promise of funding new education and transportation initiatives.

The budget that lawmakers sent to Gov. Maura Healey’s desk Monday includes a $496 million expansion to the state’s Chapter 70 funding that provides education revenue for local school districts. The money is being drawn from revenue generated by the 4% surtax on annual income over $1 million, approved by voters in 2022 through a ballot question, also called the Fair Share Amendment.

That single line item accounts for just more than 20% of the $2.4 billion in surtax spending lawmakers agreed to for the fiscal 2026 budget. It represents a shift in how that revenue is being used — and it has drawn mixed reactions even among the groups that campaigned for the surtax in the first place.

“This budget was crafted with concern over what is going on at the federal level,” Massachusetts Teachers Association President Max Page said, referring to anticipated cuts from Congress and President Donald Trump’s administration. Though the union previously warned against using surtax funds to replace routine and recurring education spending, Page said this year’s context made the decision more understandable.

“But, importantly, we certainly would hope that this much to fulfill the SOA wouldn’t be a part of next year’s budget,” he said, referring to the 2019 Student Opportunity Act, which is phasing in more than $1.5 billion in additional funding for districts over seven years. “The way it’s been working, which we really approve of, is the regular budget funds the SOA investments, and we can do new investments like higher minimum aid, universal school meals, capital fund investments, through Fair Share.”

The fiscal 2026 budget increases Chapter 70 funding by $460 million over the previous year, according to the Senate Ways and Means Committee — and funds that increase with surtax dollars. In addition to supporting the fifth year of SOA implementation, the $496 million line item for so-called SOA expansion also includes a sharp increase in minimum per-pupil aid, from $104 to $150.

In past budgets, similar increases to Chapter 70 were paid for through general state revenues. The shift this year raised red flags for those who view the surtax as a way to go above and beyond standard funding obligations.

“Voters overwhelmingly approved the Fair Share Amendment to enable new investments in public education and transportation — not to plug existing budget gaps,” said Bahar Akman Imboden, director of the Hildreth Institute, a research center focused on equity in higher education. She said she was “disappointed” to see nearly $500 million “being used to backfill” K-12 spending.

Imboden warned that reallocating surtax revenue to cover existing commitments could undermine recent progress in spending surtax dollars on higher education, which has included making community colleges free and financial aid expansions.

Those initiatives are continued in this budget, but she warned, “without corresponding investments in campus capacity, student supports, and infrastructure, the gains we’ve made in encouraging more Massachusetts students to pursue higher education will falter.”

About 11% of the surtax revenue in the fiscal 2026 budget is allocated to higher education, according to the Hildreth Institute — a roughly $5 million decrease from the previous year. On average, higher education line items saw a 0.5% increase in the fiscal 2026 budget, the Institute noted.

In previous years, surtax funds have been used to launch major new programs like universal free school meals, fare-free Regional Transit Authorities and free community college for all Massachusetts residents. Those are continued in the fiscal 2026 budget. Groups who backed the surtax saw those programs as examples of using the money for “supplementing, not supplanting” existing spending on education and transportation through general revenue.