Republican presidential hopeful Marco Rubio on Jan. 3 promised to immediately undo President Barack Obama's executive action on gun rights if he were to move into the White House in 2017.

Speaking in the critical early-primary state of New Hampshire, the Florida senator claimed Obama's move -- which will require more small-scale gun sellers to obtain federal licenses -- was unconstitutional, hours before the president had announced the details of his plan, Time reported.

"(Obama) has waged war on the Constitution," Rubio told a crowd in Raymond, New Hampshire. "He is obsessed with gun control," and the president's decision was "meant to further erode the Second Amendment."

"I believe that every single American has a Constitution -- and therefore God-given -- right to defend themselves and their families," Rubio concluded.

The White House is finalizing several measures in an effort to make progress on curbing gun violence, an issue Obama and his aides have found intractable, Politico recalled. Requiring an expanded number of small-scale gun sellers to be licensed would lead to additional background checks whenever a gun purchase takes place, the Washington publication explained.

A number of Rubio's rivals for the Republican nomination in this year's White House race, meanwhile, similarly criticized the administration's efforts. At a Mississippi campaign rally on Jan. 3, party front-runner Donald Trump promised to "unsign" anything Obama implements, CNN noted.

"There's an assault on the Second Amendment," Trump said. "You know Obama's going to do an executive order and really knock the hell out of it. ... He's going to sign another executive order having to do with the Second Amendment, having to do with guns. I will veto. I will unsign that so fast."

New Jersey Gov. Chris Christie, meanwhile, told "Fox News Sunday" that Obama "wants to act as if he is a king, as if he is a dictator."

"Fact is, if he wants to make changes to these laws, go to Congress and convince the Congress that they're necessary," Christie said. "But this is going to be another illegal executive action, which I'm sure will be rejected by the courts and when I become president will be stricken from executive action by executive action I'll take."