In the midst of a health care showdown with lawmakers at home, Gov. Charlie Baker again weighed in on federal health policy, joining nine of his colleagues on a letter to U.S. Senate leaders asking them to work with governors from both parties to find insurance reforms instead of passing a House-backed health care bill or repealing elements of the Affordable Care Act.

“The bill still threatens coverage for millions of hardworking, middle class Americans,” the bipartisan group of governors wrote to Majority Leader Mitch McConnell and Minority Leader Charles Schumer on Tuesday. “The bill’s Medicaid provisions shift costs to states and fail to provide the necessary resources to ensure that no one is left out, including the working poor or those suffering from mental illness or addiction.”

The Senate on Wednesday voted 45-55 to reject a straight repeal of the Affordable Care Act. According to media reports, the Senate may vote soon on a plan to strip the mandate that people have health insurance, a proposal that’s among the measures in a plan labeled “skinny repeal.”

“The Senate should also reject efforts to amend the bill into a ‘skinny repeal,’ which is expected to accelerate health plans leaving the individual market, increase premiums, and result in fewer Americans having access to coverage,” Baker and the other governors wrote.

Baker has since January sent a series of letters to Capitol Hill raising concerns with proposed health care policy, often joining with other governors.

State lawmakers on Wednesday rejected Baker’s proposed reforms to MassHealth, the state Medicaid program, including a shift of 140,000 low-income residents from MassHealth to subsidized commercial plans offered through the Connector.

Baker, who has been in Colorado for a Republican Governors Association gathering, is back in Boston Thursday. At 1 p.m., he plans to sign legislation establishing protections for pregnant workers.