Mike Lindell, the pillow salesman who became an enthusiastic mouthpiece for Donald Trump’s lie about a stolen election, has said he was forced to hand his phone to FBI agents who surrounded him at a fast-food drive-through.

The incident happened on Tuesday as Lindell, chief executive of My Pillow, was in line at a branch of Hardee’s in Mankato, Minnesota, his home town, following a hunting trip.

“Cars pulled up in front of us, to the side of us, and behind us and I said those are either bad guys or the FBI,” the conspiracy theorist said on his internet show, the Lindell Report. “Well, it turns out they were the FBI.”

Lindell said the agents questioned him about Tina Peters, a fellow election denier facing criminal charges in Colorado for tampering with voting machinery as a county clerk, and who in June lost a Republican primary to become the state’s top election official.

Lindell campaigned for Peters, who in May was removed by a judge from running elections in Mesa county.

An FBI spokesperson confirmed agents were “at that location executing a search warrant authorized by a federal judge” but would not give other details.

Lindell, a close Trump ally, is one of the loudest proponents of Trump’s false claims that his 2020 defeat by Joe Biden was rigged, and has been widely ridiculed for his frequent claims that he has enough “evidence” to see Trump reinstated to the presidency.

Lindell admitted earlier this month that he had spent up to $40m of his own money in the pursuit, including underwriting lawsuits in numerous states to try to eliminate voting machines he insists were to blame for Trump’s defeat.

There is no evidence to support his allegations and Lindell has lost numerous legal challenges over machines manufactured by Smartmatic and Dominion.

In April, he was sued for defamation by a Dominion Voting Systems employee, who claimed Lindell was engaged in “efforts to undermine faith in American democracy and enrich himself in the process”.

Lindell said on Tuesday the FBI demanded his phone, which he handed over only after consulting his attorney.

“They surrounded me at a Hardee’s and took my phone that I run all my business, everything with,” he said. “What they have done is weaponise the FBI, it’s disgusting. I don’t have a computer, that phone, everything was on everybody.”

In a later interview with CNN, Lindell said he was surprised when the agents started asking questions about Peters, having assumed they were about to serve him a subpoena as part of the justice department investigation into the 6 January insurrection and other attempts to reverse Trump’s election defeat.

“I said, ‘Come on, bring me to January 6. I want to be part of that show’,” he said he told them.

“They thought they were there to intimidate me. They won’t intimidate me.

“I want to say this for the record, they were pretty nice guys. None of them had an attitude.”