PHOENIX — Six months after Gov. Jan Brewer pushed an expansion of Arizona's Medicaid health insurance program through the Legislature, a lawyer for the Republican governor asked a judge Friday to block an effort by GOP lawmakers to block the law.

Attorney Douglas Northup told Maricopa County Superior Court Judge Katherine Cooper that the lawmakers lost fair and square and she shouldn't allow them to "ask you to go down a very slippery slope," that could lead any lawmaker who lost a vote to run to the courthouse.

The lawmakers, 36 in all from both chambers, argue that the expansion plan Brewer shepherded through the Legislature in June violates the state Constitution because it raised taxes without a required two-thirds vote. Goldwater Institute attorney Christina Sandefur, representing the lawmakers and three citizens, said the coalition of Democrats and Republicans that Brewer assembled to push the plan through didn't meet that threshold and the opponents' votes were "nullified." The law includes a "hospital assessment" that will pay the state's share of costs.

Cooper appeared to struggle with the idea that lawmakers who lost a vote could come to court to challenge the resulting law.

"I guess I don't understand what you mean by nullifying," Cooper said. "They voted, the vote counted and there weren't enough votes to support your clients' position," Cooper asked.

"The Arizona Constitution empowers one-third plus one of the legislators to stop any sort of tax or tax increase," Sandefur responded. "These plaintiffs had enough votes to defeat this legislation. Therefore their votes have been nullified."

Northup reminded Cooper that lawmakers refused three times to add a section to the law designating the assessment as a tax requiring a two-thirds vote.

The issue Friday was just the opening salvo in what could be a lengthy court challenge. Cooper said she would try to rule on whether to allow the case to proceed by the end of the year.

The hospital assessment is expected to collect $256 million in the state's 2015 budget year to pay the state's share of expanding Medicaid to about 300,000 people who earn between 100 percent and 138 percent of the federal poverty level. Coverage begins Jan. 1. Hospitals strongly backed the assessment because they expect to see a much bigger reduction in the cost of treating uninsured patients.

If the lawmakers are allowed to pursue the lawsuit and win, the Medicaid expansion would remain in place but the mechanism that brings in cash to match billions in federal spending would be lost.

Brewer is one of only a handful of Republican governors who embraced Medicaid expansion, a key part of President Barack Obama's health care overhaul law. In all, 25 states plus Washington, D.C., are moving ahead with the expansion, while 19 states have turned it down. Another six states are still weighing options.

Another Republican governor who pushed expansion, John Kasich of Ohio, is also facing a court challenge after he bypassed Republican opponents in the Legislature who opposed Medicaid expansion. Kasich instead brought a request to spend billions in federal money to expand the program to a powerful Legislative panel, where he needed fewer votes than the full General Assembly. Opponents are asking the Ohio Supreme Court to void that vote.

In Arizona, Brewer spent months trying to get Republicans who control both chambers to support Medicaid expansion. She convinced a handful of Republicans to join all minority Democrats and put together a majority that supported the move, but leaders refused to let it come to a vote. She finally rammed it through in June after calling a special session to get around recalcitrant GOP House and Senate leaders.