Several Republicans threatened to use Congress’s annual spending bills to hit back at gun control policies announced by President Obama on Tuesday, furious at the president’s attempt to sidestep Congress on such a controversial issue.

Leading Republicans on the House Appropriations Committee and from the party’s conservative wing vowed to use the appropriations process to block Obama’s executive actions and deny the president the necessary funding to implement some of his proposals.

“What the president has done is unconstitutional and any action Congress can take, we should, including appropriations,” said Rep. Ken Buck (R-Colo.) a member of the House’s Freedom Caucus.

In the meantime, some Republicans are exploring options beyond the appropriations process to combat the president’s latest actions.

“I don’t have any faith that when it comes down to negotiations between the two sides that this will be addressed,” Buck said, adding that he hopes Senate Republicans will stage a protest by refusing to confirm Obama’s nominees.

Spokesmen for Freedom Caucus founders Jim Jordan (R-Ohio) and Matt Salmon (R-Ariz.) said those congressmen would likely also be on board.

The response by Republican leaders, especially Speaker Paul Ryan (R-Wis.), was equally indignant but less specific. The issue could prove a key test of whether Ryan can satisfy the conservative wing in his first full year after replacing then-Speaker John Boehner (R-Ohio).

But Republicans’ only real shot at diluting Obama’s executive actions is during the budget process, which will not come to conclusion until early fall because of the budget deal struck last year by lawmakers. Some of Obama’s proposals may rely on lawmakers to approve funding for them, including hiring an additional 230 FBI examiners to process background checks and 200 new Bureau of Alcohol, Tobacco, Firearms and Explosives investigators to enforce current laws. Congress would also have to approve devoting $4 million to track illegal online gun trafficking and dedicating $500 million to improving mental health services.

“The Committee is very concerned about the implications of this proposal, and will take a careful look at the funding as we move forward with the next budget cycle,” said Jennifer Hing, a spokeswoman for House Appropriations Committee Chairman Hal Rogers (R-Ky.).

On Tuesday in an emotional news conference, Obama announced a roster of executive actions designed to decrease gun violence, including expanding background checks by mandating licenses for people who sell guns on the Internet or at gun shows, requiring that lost or stolen guns be reported to federal authorities and promoting the development of better safety triggers to prevent accidental shootings.

Ryan and Senate Majority Leader Mitch McConnell (R-Ky.) both panned Obama’s proposals, but did not specify how Congress should respond.

“From day one, the president has never respected the right to safe and legal gun ownership that our nation has valued since its founding,” Ryan said in a statement. Ryan, like McConnell, promised committees will closely examine the proposals but did not detail further possible actions.

“Ultimately, everything the president has done can be overturned by a Republican president, which is another reason we must win in November,” McConnell said.

But rank-and-file Republicans may be looking for a more immediate and visceral response.

The appropriations strategy was launched Monday by Rep. John Culberson (R-Texas), who chairs the House Appropriations Committee’s subcommittee overseeing the Justice Department. In a letter to Attorney General Loretta Lynch, he warned that “the House Appropriations Committee will not provide resources to your Department for the development or implementation of unlawful limitations on the unambiguous Second Amendment rights of Americans.”

But as Culberson noted in a statement, there are still several months to go in the current fiscal year. That means Congress could have to wait until the beginning of October before using the appropriations process to try and block the executive actions.

“We passed that omnibus and gave up our leverage,” Republican presidential candidate Sen. Rand Paul (R-Ky.) said, referring to the year-end spending bill signed into law last month. “If we had courage and guts, which most of the time we do have, we could vote on a new spending bill which blocks funding for new gun control orders. That was why so many of us thought the omnibus was a bad idea.”

The issue of gun control has divided Congress down party lines, with only a smattering of Democrats and Republicans willing to work on bipartisan proposals. The most recent test came last month, when the Senate rejected amendments to an Obamacare repeal bill that would have expanded background checks for gun purchases online or at gun shows and restrict people whose names appear on terror watch lists from purchasing firearms.

Even Republicans who supported some of those measures are now balking at Obama’s move to implement what are arguably less far-reaching changes.

“This president has a habit of going off and doing it on his own when he doesn’t get his way,” said Sen. Pat Toomey (R-Pa.), who along with Sen. Joe Manchin (D-WVa.) wrote the proposal to expand background checks in a 2013 bill that also received a vote last month.

Manchin also objected to Obama’s moves, stressing the need for the president to go through Congress.

“Instead of taking unilateral executive action, the President should work with Congress and the American people,” Manchin said in a statement released Tuesday. “Like all law-abiding Americans and gun owners, I want to prevent future incidents of gun violence and keep firearms out of the hands of criminals and the mentally ill, but legislation and consensus is the correct approach.”

Republicans opposed to Obama’s gun proposals routinely call on the administration to instead focus on mental health, arguing that enhanced background checks wouldn’t have prevented most of the recent mass shootings.

“If the President would roll up his sleeves and work with the bipartisan coalition in Congress who support legislation reforming our mental health system, together we could help prevent many of these tragedies from happening in our communities,” said Senate Majority Whip John Cornyn (R-Texas), the sponsor of one of several mental health bills wending their way through Congress.

Obama challenged Republicans to embrace his executive action on mental health, calling on those who have clamored for similar policies “put your money where your mouth is.”

Rep. Tim Murphy (R-Pa.), who has written mental health legislation, said in an interview that the $500 million in mental health funding “could be good, but it depends on where it goes.”

Colby Itkowitz and Dave Weigel contributed to this report.