A Montana Republican lawmaker who says the US constitution allows for socialists to be jailed or shot will only resign “if God asked me to”.

State representative Rodney Garcia, of Billings also said he has been congratulated by supporters for his controversial stance and has filed to run for state senate.

Garcia made his claim at an event featuring former interior secretary Ryan Zinke on Friday, then stood by it after a Billings Gazette report attracted national attention.

He was rebuked by his party and three Republican legislative leaders called on him to resign over remarks they called “un-American”.

But Garcia remained unrepentant, saying socialism, which he called “pretty much communism”, is dangerous.

Speaking to the Associated Press, Garcia said he had received some threats. “They can’t come up to me and talk to me,” he said, “but they want to shoot me. That’s fine, but if you miss, I won’t.”

Socialists “have to be tried, and if they’re found guilty” they can be jailed or shot, he insisted. “But more than likely they would never be shot because we just don’t do that in today’s society. We’re supposed to be civilized.”

As previously, Garcia could not cite which part of the constitution supports his claims. Section 3 of article III deals with treason but says: “Treason against the United States, shall consist only in levying War against them, or in adhering to their Enemies, giving them Aid and Comfort.”

Socialism is in the national news in the US. Bernie Sanders, a frontrunner for the nomination to face Donald Trump in the presidential election in November, describes himself as a democratic socialist.

Garcia’s Democratic opponent in his last election was Amelia Marquez, a trans Sanders supporter who also describes herself as a democratic socialist. On Tuesday she called him “Rodney ‘Shoot-the socialist’ Garcia” and called for donations to the incumbent senator, Democrat Margie MacDonald.

Trump has made allegations of socialism on the part of the entire Democratic party a key part of his early re-election campaign. Garcia’s comment about socialism being “pretty much communism” echoed remarks by the president in a Sunday interview with Fox News host Sean Hannity.

The president said: “I think of communism when I think of Bernie … I think of Bernie sort of as a socialist but far beyond a socialist.”

On Monday, Montana House speaker Greg Hertz, speaker pro tempore E Wylie Galt and majority leader Brad Tschida wrote to Garcia, calling his “inflammatory remarks … deeply disturbing” and saying he had refused a request to retract them.

They wrote: “Your reckless and un-American remarks are beneath that of a public official and do not represent the values of the Republican party, Montana House of Representatives or the people of our great state.

“Your actions have irreparably undermined the body in which you serve and irrevocably broken the trust of those you were elected to represent. We believe it is clear that you can no longer effectively discharge the duties of the office you hold; therefore, it is our request that you submit your resignation with immediate effect.”

Garcia told the AP: “They can ask me to step down but no, I don’t think so. I’m going to run for the Senate and I’m going to win. People are going to have to eat their words.”

Saying none of the party leaders who attended the Zinke event said anything at the time, he added: “I’m getting my head so big from people saying, ‘Thank you, Rodney, for bringing this up.’

“If people don’t want me in the Senate they can say: ‘Well, I’m not going to vote for ya.’ That’s their prerogative.”