A lengthy list of proposals unveiled by the Charlie Baker administration last week includes significant changes to the state Medicaid program. Matthew J. Lee/Globe staff

Governor Charlie Baker has been a vocal opponent of Republican legislation in Congress that would sharply curtail Medicaid funding, cuts that would hit the state’s poor, disabled, and elderly residents.

But a lengthy list of proposals unveiled by the Baker administration last week includes significant changes to the state Medicaid program, known as MassHealth, that many advocates say would also hurt low-income working parents.

One significant change would allow the administration to shift about 140,000 adults, including 100,000 parents, from MassHealth to commercial insurance plans on the state Health Connector. The state and federal governments would subsidize their premiums, but the policies would have less generous coverage and higher out-of-pocket costs.

Under Baker’s plan, which would not affect people with disabilities, adults in two-person households making between $16,240 and $21,600 a year would become ineligible for MassHealth. Parents in this income bracket have been allowed to enroll in MassHealth for 20 years.

The administration also wants to put up a “gate” that prevents many low-income adults with access to employer-sponsored health insurance from obtaining MassHealth. Advocates say this proposal, too, would hit working families who can’t afford to pay premiums.

Administration officials, who need approval from the Legislature and federal officials in order to carry out several of the proposals, said the changes are necessary to control spending. They said legislators asked them to devise solutions to deal with the soaring costs of MassHealth, so the package — which is expected to save the state hundreds of millions of dollars — should not come as a surprise.

MassHealth represents the biggest chunk of the state budget, and its rolls have been growing. More than one in four state residents is covered under the program, which is jointly funded by state and federal tax dollars.

Brian Rosman, policy director at the Boston-based advocacy group Health Care For All, said low-income parents have long relied on MassHealth. “To say that they will be moved to Connector programs or they will be totally out of luck if they have employer coverage — for very little savings — we think is harmful,” he said.

The administration’s plan would impose a much-discussed new fee on employers to help pay state health care costs. It also calls for limiting the number of similar prescription drugs covered by MassHealth, creating a new mid-level care provider called a dental therapist, strengthening requirements for tiered insurance plans, and several other measures.

The overhaul package was dropped on legislators last week as they worked behind closed doors to complete a state budget for the fiscal year that begins Saturday — an unusual move that mystified many lawmakers and advocates. The administration asked legislators to include the series of health care proposals in their final budget, although many of the changes have seen no public debate.

The Legislature is expected to vote on a budget plan within days.

“Making this kind of drastic change, which will primarily affect low-income parents, seems like a really unwise step to take, much less a change to make with a week’s notice,” said Victoria Pulos, a health care lawyer at the Massachusetts Law Reform Institute.

Pulos said the administration appears to be pulling back provisions of the federal Affordable Care Act that expanded Medicaid coverage to more adults — even as the governor has advocated strongly for keeping key features of that law. Republicans in Congress are seeking to dismantle it.

“We definitely appreciate the efforts of the governor . . . to protect the Medicaid program at the federal level, but it seems very inconsistent with that position,” Pulos said of Baker’s latest health care proposals.

The Baker administration wants authority to cut certain “optional” MassHealth benefits, Pulos said, which is also raising concerns.

“[There are] cuts to MassHealth and changes to MassHealth eligibility that particularly harm low-income working parents,” said state Representative Christine P. Barber, a Somerville Democrat and member of the House Progressive Caucus. “We just saw these changes last week and haven’t had time to process them.”

Administration officials said they designed their proposals to respond to requests from both the House and Senate to address the MassHealth budget. Their package helps residents stay covered while protecting taxpayers, and it has the support of many in the business and health care community, they said.

They said they will seek public comments on the planned changes, as required, when they file their plans with the federal government.

“All this stuff is going to go through what I would describe as a public process,” Baker told the Globe after visiting an education and job training center in downtown Boston on Thursday.

“This has been part of an ongoing conversation with folks in the health care community, the business community, and the insurance community for the past several months,” he added.

The 140,000 adults whom the administration wants to move off MassHealth would be able to enroll in health plans in which they pay no premiums. But they would have to pay higher co-pays and other out-of-pocket costs, totaling a maximum of $2,500 per family. The change, if approved, would begin in 2019.

By leaving MassHealth, these adults also would lose dental coverage. They could purchase a separate dental plan or get dental care at a community health center, where they would be reimbursed, the administration said.

House and Senate leaders have signaled support for the administration’s proposed new fee on employers to help pay the costs of MassHealth, but they have not said how they will vote on the other health care proposals, including changes to the program’s eligibility rules.

A conference committee of House and Senate members was still finalizing the budget Friday.

“The Governor’s health care proposal is extensive and complex,” the Senate’s budget chief, Karen E. Spilka, said in a statement. “We are hearing from advocates and legislators who are doing their best to weigh in at this late hour. They are raising concerns about the limited time they had to review and provide input on provisions that were not part of the budget.”