Rep. Matt Rosendale (R-Mont.) ticked up his opposition to House Minority Leader Kevin McCarthy’s (R-Calif.) Speakership bid in an op-ed on Wednesday, leaving little room for the possibility that he could support McCarthy for Speaker on the House floor next year.

“If Kevin McCarthy couldn’t lead in the minority, he doesn’t have the ability to serve as speaker of the House,” Rosendale said in the op-ed for the Billings Gazette. “We need a speaker who is strong enough to get things done with a Democrat-controlled White House and can unite the Republican party. You didn’t elect me to be a rubber stamp. We cannot continue to do the same thing with the same people and expect a different outcome. My promise is to always fight for Montanans while in Washington.”

He cited McCarthy’s resistance to proposed rules changes, like streamlining single-issue bills and opening the amendment process on the House floor, as reason for opposition. He also charged that McCarthy did not do enough to leverage must-pass spending bills to secure conservative priorities.

Rosendale is part of a group of five vocal House Republicans who have explicitly said or strongly indicated they will not support McCarthy for Speaker on Jan. 3. That other lawmakers are GOP Reps. Andy Biggs (Ariz.), Matt Gaetz (Fla.), Ralph Norman (S.C.) and Bob Good (Va.). With Republicans heading into the 118th Congressional session with a slim majority, that opposition has the potential to derail McCarthy’s bid for Speaker.

Unlike the other four, though, Rosendale has not explicitly committed to voting for an alternative candidate. He has previously said he could only vote for McCarthy under “extreme circumstances,” but has also said he will not vote “present” during the Speakership vote, a move that would have potentially given McCarthy more breathing room in the Speaker vote. McCarthy needs support from a majority of those voting for a specific candidate to win the gavel.

Rosendale also expressed resistance to McCarthy in a tweet last month after McCarthy was nominated by House Republicans to be Speaker, which the GOP leader won in a 188 to 31 vote over a protest challenge from Biggs.

“He wants to maintain the status quo, which consolidates power into his hands and a small group of individuals he personally selects. We need a leader who can stand up to a Democrat-controlled Senate and President Biden, and unfortunately, that isn’t Kevin McCarthy,” Rosendale said.

Rosendale is considered to be a possible challenger to Sen. John Tester (D-Mont.) in 2024.