The Alaska Legislature on Tuesday said it will sue Gov. Bill Walker to block his move last month to expand the public Medicaid health care program without lawmakers' approval.

Following a private discussion Tuesday morning, a Republican-controlled House-Senate committee voted 10-1 to spend up to $450,000 on two law firms to represent the Legislature in a suit against the governor.

One, Bancroft PLLC, is based in Washington, D.C., and represented more than two dozen states in their U.S. Supreme Court challenge to the Affordable Care Act, or "Obamacare." The second, Holmes, Weddle & Barcott, is based in Anchorage.

In a news conference after the committee vote, Republican leaders framed their decision to challenge the governor as a constitutional one. They're seeking an injunction to stop Medicaid expansion from going into effect Sept. 1.

"This is not a policy issue — we're not discussing whether we should or shouldn't expand Medicaid," said Senate President Kevin Meyer, R-Anchorage. "This is a question of authority and process and our constitution."

Asked about the impact of their decision on Alaskans without access to health care, Senate Majority Leader John Coghill, R-North Pole, responded: "They have access to health care."

"It's just more costly, and there are other ways they can get health care," he added.

The Legislature's decision is the latest development in a battle with Walker over Medicaid expansion that's now lasted for seven months — since the beginning of the legislative session in January.

The governor, a Republican-turned-independent, promised to expand Medicaid during his campaign last year, which saw him endorsed by the state Democratic Party.

Walker's administration says the expansion would make some 40,000 low-income residents newly eligible for Medicaid and actually reduce Alaska's budget by replacing state money with federal funding.

But during the legislative session, when Walker put expansion language into his initial budget, Republican lawmakers stripped it out, saying the governor should submit standalone expansion bills to the House and Senate so they could properly vet the proposal.

He did that, but the Republican co-chairs of the finance committees never brought the bills to a vote.

Lawmakers at their Tuesday news conference said they still needed more time to examine the issue because of the risk of Medicaid's costs in the future — at the same time the state is facing multibillion-dollar deficits and quickly spending its savings.

They've cited reports that Medicaid enrollment under Obamacare has exceeded projections in other states, with lawmakers elsewhere warning that health care spending is threatening to pull money away from other areas like education.

But Walker, in a hastily organized news conference afterward, suggested the opposition was political. He called the Legislature's decision to bring the lawsuit "totally unacceptable" and said it "makes no sense at all to me."

"I cannot fathom why suing to take away health care coverage of working Alaskans is a partisan issue," he said.

Walker estimated the lawsuit would cost the state $1 million based on the anticipated cost of legal work necessary to defend the expansion, and he said his administration would move ahead with its initiative unless the Legislature gets an injunction.

The 10-1 vote Tuesday was taken by the Legislative Council, a joint House-Senate committee that handles business and budgets for the Legislature when all 60 members aren't in session.

It came after a 75-minute meeting in "executive session" from which the public was barred so lawmakers could get legal advice. Staff members were spotted afterwards carrying a printed presentation prepared by Coghill's office titled "The Case Against Gov. Walker's Attempt at Unilateral Medicaid Expansion."

All the members of the Republican-led majority caucuses who were present sided against the committee's lone Democratic minority member, Juneau Rep. Sam Kito.

Voting in favor of hiring the two law firms were Republican Reps. Mike Chenault of Nikiski, Steve Thompson of Fairbanks, Craig Johnson and Charisse Millett of Anchorage and Mark Neuman of Big Lake, Democratic Rep. Bob Herron of Bethel, and Republican Sens. Anna MacKinnon of Eagle River, John Coghill of North Pole, Charlie Huggins of Wasilla and Kevin Meyer of Anchorage.

Two Republican senators from coastal areas typically viewed as more moderate, Gary Stevens of Kodiak and Peter Micciche of Soldotna, were absent, as was Sen. Lyman Hoffman, D-Bethel, who belongs to the Senate's Republican majority.

Rep. Mike Hawker, R-Anchorage, also missed the meeting. He was in Minnesota undergoing medical treatment but said by email he would have voted against hiring the law firms.

Last month, after Walker announced he was pursuing Medicaid expansion unilaterally, Hawker said the move was "fully and completely within his constitutional and statutory authority."

The governor is seeking to expand Medicaid using an established committee process that allows lawmakers to make recommendations on — but not to block — the state's receipt of federal money.

Under the ACA, the costs of Medicaid expansion are paid entirely by the federal government through 2016 before scaling back to 90 percent by 2020.

The Legislature is challenging Walker's move based on a provision in Alaska statute that requires legislative approval before Medicaid coverage can be offered to people whose care is not required under federal law.

The version of "Obamacare" passed by Congress required states to expand Medicaid to cover low-income Americans, who can otherwise face steep health care costs without the subsidies that the legislation offers to individuals with higher incomes.

As written, the law would have revoked all federal Medicaid funding for states that didn't go through with the expansion. But the U.S. Supreme Court said in 2012 that the threat of revoking the money was unconstitutional and coercive.

The ruling created ambiguity for Alaskan policymakers and legal experts: If Medicaid expansion is technically required under the ACA, but the Supreme Court has ruled the federal government can't enforce the requirement by revoking money from states that don't comply, does that make the newly eligible people under Walker's proposed expansion an optional group that requires legislative approval?

Walker, citing a memorandum from Attorney General Craig Richards, says no. The Republican lawmakers that support the lawsuit say yes and argue the governor is circumventing their authority.

An initial filing in the Legislature's lawsuit is expected next week.

Correction: An earlier version of this story incorrectly reported that the Legislature did not take up the issue of Medicaid expansion during its two special sessions earlier this year. In fact, lawmakers held hearings on the topic in May, though they did not take a vote.