Republican lawmakers hit back on President Barack Obama’s plans to unveil a series of executive actions this week aimed at tightening gun laws.

Ahead of Obama’s meeting Monday with top law enforcement officials to finalize expanded gun control measures, House Speaker Paul Ryan called the president’s extent of executive overreach “dangerous.”

“While we don’t yet know the details of the plan, the president is at minimum subverting the legislative branch, and potentially overturning its will,” Ryan, R-Wis., said in a statement.

House Majority Leader Kevin McCarthy criticized Obama on Twitter, writing that his plan “poses a grave threat” to the separation of powers and charged that the president is attempting to “legislate from the executive branch.”

Obama met with Attorney General Loretta Lynch Monday to discuss the administration’s options for strengthening gun control after several months of internal legal review.

He said the recommendations from his cabinet were “well within” his legal authority and “entirely consistent with the Second Amendment.”

“We have to be very clear that this is not going to solve every violent crime in this country, it’s not going to prevent every mass shooting, it’s not going to keep every gun out of the hands of a criminal,” Obama said.

For the United States to fully address gun violence, he said, “Congress needs to act.”

The key proposal Obama is expected to announce would allow the president to sidestep Congress to require more gun dealers to obtain a federal license and conduct background checks on customers purchasing firearms.

The shift would expand the definition of who is considered a firearms dealer under federal law, encompassing a broad number of people who are currently exempt to force more sales on government records.

The administration hopes the change will capture unregistered dealers who escape background checks by selling at gun shows, online, and at other venues not covered under law.

The White House is also set to implement stricter requirements on reporting lost and stolen weapons, a measure the Bureau of Alcohol, Tobacco, Firearms and Explosives advocated for in 2014 but failed to pursue against gun advocates, who claimed that voluntary reporting was adequate.

Ryan said none of Obama’s proposals would have prevented the recent mass shootings in the U.S. and that the focus should instead be on addressing mental illness.

“His proposals to restrict gun rights were debated by the United States Senate, and they were rejected,” Ryan said. “No president should be able to reverse legislative failure by executive fiat, not even incrementally.”

Congress blocked expanded background checks in 2013. House Republicans said the president’s latest decisions on gun control overstep his authority.

Obama revived steps toward enacting steeper gun control measures in October following the fatal shooting at Umpqua Community College that left nine dead.

In his weekly address released New Year’s Day, Obama said his 2016 resolution was to move forward on “unfinished business”—specifically, the U.S.’s “epidemic of gun violence.”

He is expected to release specific details of the plan during a town hall Thursday at George Mason University.

“We know that we can’t stop every act of violence. But what if we tried to stop even one? What if Congress did something—anything—to protect our kids from gun violence?” Obama said.

Current law requires anyone who is “engaged in the business” of dealing firearms to be federally licensed, thus requiring the seller to perform background checks.

But the law is vague in defining who is considered a gun dealer, exempting anyone “who makes occasional sales, exchanges, or purchases of firearms for the enhancement of a personal collection or for a hobby, or who sells all or part of his personal collection of firearms.”

The administration’s measure would clarify who is considered “in the business” of selling guns, requiring that anyone who sells a specific number of guns register with the ATF and conduct background checks.

Sen. Marco Rubio, R-Fla., said Sunday the president’s planned executive actions would undermine the rights guaranteed under the Second Amendment, remarking that Obama has “waged war on the Constitution.”

“Law-abiding gun owners are not the problem in this country. The problem are criminals, and criminals don’t care what laws you pass,” Rubio said. “You can pass all the gun laws in the world that you want. It will not stop the criminals.”