Leading US Republicans have denounced President Barack Obama’s move to tighten gun controls.
House of Representatives Speaker Paul Ryan said the executive orders, which bypass Congress, “undermined liberty” and would be challenged in court.
Republican presidential frontrunner Donald Trump said that, if elected, he would reverse the measures.
In an emotional address on Tuesday, Mr Obama accused the gun lobby of holding the country hostage.
Wiping away tears, he recalled the 2012 Sandy Hook primary school shooting in which 20 children and six adults were killed.
However, the largest gun lobby group, the National Rifle Association (NRA), said Mr Obama’s steps would not have prevented any recent mass killings in the US.
“Rather than focus on criminals and terrorists, he goes after the most law-abiding of citizens,” said Mr Ryan, a Republican.
“His words and actions amount to a form of intimidation that undermines liberty.”
Correspondents say the announcement is already shaping up to be an issue in the 2016 presidential election.
Donald Trump said that he would “un-sign” the measures if elected to the White House - a sentiment echoed by other Republican presidential candidates.
Senator Ted Cruz tweeted that the executive actions were unconstitutional, with a link to sign up for his campaign correspondence on a web page that says “Obama wants your guns”.
Former Florida governor Jeb Bush, also a Republican candidate, tweeted that he would repeal the actions and protect the Second Amendment.