JUNEAU — A state court judge in Alaska on Tuesday upheld Gov. Bill Walker’s decision to expand Medicaid without legislative approval, finding that the federal Social Security Act requires Medicaid expansion.

Superior Court Judge Frank Pfiffner dismissed a challenge to Walker’s authority by the Legislative Council, which is comprised of state House and Senate lawmakers. That decision can be appealed.

A spokeswoman for the Senate majority said the Republican-led majority is looking over the decision and will evaluate its options. The decision came as Republicans in Alaska were participating in the state’s presidential preference poll.

A key argument in the case centered on whether the expansion population is a mandatory group for coverage under Medicaid or an optional group that cannot be covered unless approved by the Legislature. The Legislative Council, in its lawsuit, argued that Walker overstepped his authority in expanding Medicaid on his own.

The federal health care law expanded eligibility for Medicaid, and the U.S. Supreme Court in 2012 upheld most of the law. But it also found that states cannot lose existing Medicaid funding if they don’t expand Medicaid coverage.

Pfiffner found that the U.S. Supreme Court decision striking down a penalty for not complying with expansion did not affect the requirement that states provide Medicaid to the expansion group.

“This requirement may lack the coerciveness that Congress intended, but it is still a requirement,” Pfiffner wrote.

The Legislature can change state law to reject the expansion if it wants, he wrote. Until then, state law requires the governor to provide Medicaid services to the expansion group, Pfiffner wrote.

The population targeted by expansion is people between the ages of 19 and 64 who are not caring for dependent children, not disabled and not pregnant, and who earn up to 138 percent of the federal poverty level.

Expansion in the state took effect last September. More than 10,000 people have been covered by the expansion, according to the state health department.

Walker, in a statement, said he is pleased with the decision. He said the administration would continue to work with the Legislature on efforts to redesign and reform the Medicaid program.