The Supreme Court faces a momentous decision on the sweeping health insurance reform law that President Obama wants to leave as part of his legacy. (Karen Bleier/AFP/Getty Images)

Attorneys for the Obama administration and the Republican-controlled House of Representatives clashed Thursday over whether a federal judge should toss out a lawsuit by lawmakers accusing the president of exceeding his executive authority in unilaterally implementing portions of the Affordable Care Act health law.

The suit was approved by the U.S. House of Representatives on a party-line vote last July and filed in U.S. District Court in Washington. It focuses on the administration’s decisions to pay subsidies to insurance companies that they say were not authorized by Congress and to twice waive the deadline for the so-called “employer mandate” requiring larger employers to provide health insurance to employees.

“The House cannot sue the executive branch over the implementation of existing federal law,” said Justice Department attorney Joel S. McElvain, urging U.S. District Judge Rosemary M. Collyer to dismiss the case.

McElvain called Congress’s complaint legally invalid and unprecedented in asking the courts to referee a political dispute it could resolve by revoking the law, passing new legislation, withdrawing funding or rejecting nominees, among other things.

“There are any number of other tools the legislature can use to influence the executive branch . . . which is why we have not seen a lawsuit like this in over 230 years,” McElvain said.

House Speaker John A. Boehner (R-Ohio). (Susan Walsh/AP)

Attorneys for the House argued that it rejected an administration request for funding in 2014 for the relevant subsidies, but that the Obama administration went ahead anyway. The administration claims that it withdrew its request because the subsidies were covered by an earlier permanent appropriation.

The administration’s argument would mean that Congress’s constitutionally designated “power of the purse is effective decorative,” argued George Washington University law professor Jonathan Turley.

“There could not be more serious stakes,” said Turley, who took up the House’s case after two other attorneys declined. “The administration has committed $175 billion without congressional approval.”

After the 90-minute hearing, Collyer, a 2003 George W. Bush appointee, said she did not know how or when she would rule.

“I just haven’t decided yet,” Collyer said, after praising the rigor of both sides’ arguments. “We will get to work on it.”

The politically sensitive case comes as both sides await a decision by the U.S. Supreme Court in a separate lawsuit, King v. Burwell, over whether the Obama administration is illegally granting tax subsidies to millions of individual Americans who buy health insurance in federal exchanges. The total includes an estimated 7.5 million people in 34 states where authorities have declined to establish their own exchanges.

The House GOP lawsuit, aimed at the Treasury and Health and Human Services departments, takes another tack.

The suit, House of Representatives v. Burwell, challenges the constitutionality of billions in subsidies to insurance companies that the government expects to issue over 10 years on behalf of taxpayers who sign up for coverage in federal or state-run health exchanges.

The complaint also attacks a provision that the House agrees with in spirit.

The House has voted to postpone the employer mandate. However, it argues the administration’s move to unilaterally delay enforcement of the provision lacked legal authority.

In a statement issued before Thursday’s hearings, House Speaker John A. Boehner (R-Ohio) called the two actions “two egregious examples that undermine the separation of power.”

“Time and again, the president has chosen to rewrite the law whenever it suits him, ignoring the will of the American people and the Constitution itself,” Boehner said. “No one — especially no president — is above accountability to the Constitution and the rule of law.”

President Obama at the time of the House vote dismissed the lawsuit, saying the existing law is helping Americans.

“Everyone sees this as a political stunt, but it’s worse than that because every vote they’re taking . . . means a vote they’re not taking to help people,” Obama said.