(Reuters) - Washington state Republican lawmakers urged one of their own to resign after a state report found that he engaged in “domestic terrorism” against the United States by participating in armed conflict through the right-wing militia movement.

Representative Matt Shea was a leader in the Patriot Movement defying federal authority in Nevada, Idaho and Oregon in 2014, 2015 and 2016, according to a report by the private Rampart Group commissioned by the Washington state House of Representatives and released on Thursday.

One of those actions involved a 41-day standoff at an Oregon wildlife refuge that resulted in one death, the report said.

“Representative Shea participated in an act of domestic terrorism against the United States by his actions before and during the armed takeover and standoff at the Malheur National Wildlife Refuge,” the report said, using a definition under U.S. law.

The Republican House leadership immediately called for Shea’s resignation and suspended him from the party caucus. The chief clerk of the House referred the matter to the FBI and U.S. attorney’s office, J.T. Wilcox, the Republican leader in the House, said in a statement.

“He should resign,” Wilcox said separately on Twitter.

Shea, who has been a member of the House since 2009, vowed to remain in his post, comparing the effort to oust him to the impeachment of President Donald Trump.

“I will not back down, I will not give in, I will not resign,” Shea said on Facebook. “Stand strong fellow Patriots.”

The militia movement expresses deep mistrust of the federal authority and disdains the regulation of firearms.

In 2014, Shea participated in an armed standoff in Nevada, led by rancher Cliven Bundy, who insisted on the right to let his cattle graze on federal lands without paying fees, the report said.

In 2015, the report said, Shea engaged in another conflict in Idaho in support of a military veteran who defied a lawful order to surrender his weapons.

In 2016, Shea helped plan another uprising by Ammon Bundy, the son of Cliven Bundy, who took over a national wildlife refuge in Oregon for 41 days, causing great stress on local communities, the report said.

“There are scars and wounds left by the threats and intimidation that were so prevalent during this time that they may never heal,” Craig LaFollette, the former mayor of Burns, Oregon, said in an email.

The report cited other instances of Shea’s condoning violence, intimidating political opponents and promoting militia training to confront law-enforcement agencies.