Congressional Republicans have joined in a lawsuit challenging President Barack Obama’s recess appointments to the National Labor Relations Board in January, a legal fight focused on the constitutional limits of presidential appointment power.

Senate Minority Leader Mitch McConnell, R-Kentucky, and 41 other Republican senators filed an amicus brief Wednesday in the case of Noel Canning, a company challenging whether the appointments were unconstitutional.

Obama angered Senate Republicans with his recess appointments during a two-day break between pro forma sessions that even some constitutional lawyers concluded didn’t qualify as an actual recess. Republican retaliation came this year at the expense of Obama’s judicial nominees.

Now the senators are following through on a promise to legally challenge the appointments.

The brief filed by Miguel Estrada, a partner with Gibson, Dunn & Crutcher in Washington, argues Obama’s actions deprive the Senate of two powers: The authority to govern its own proceedings and the ability to reject presidential appointments.

“By declaring the Senate not ‘capable’ of performing its constitutional function and therefore in a de facto period of ‘recess,’ even while the chamber decided to be in session repeatedly, the president usurped the Senate’s control of its own procedures,” the brief states. “Most remarkable of all, however, is that the president asserted this novel power when he did: in between pro forma Senate sessions that he and Congress alike have long accepted as valid.”

The most outspoken critic of Obama’s recess appointments — which included Richard Cordray of the Consumer Financial Protection Bureau and three members of the NLRB — was Senator Mike Lee, R-Utah. He said in March that he would oppose all judicial nominees “until such action is taken to ensure that the Senate’s constitutional right to advise and consent to nominees is properly respected.”

House Speaker John Boehner, R-Ohio, also filed an amicus brief on Wednesday, prepared by Jay Sekulow, chief counsel for the American Center for Law and Justice.