A progressive group is calling for the election of a Republican to the United States Senate after Republican officials and outside groups said they were planning to challenge his bid for the seat.

An advocacy group, Indivisible, said it would help with the election effort.

Irvine, a former state senator from Northern California, was endorsed by Republican Sen. Richard Burr of North Carolina and Democratic Sen. Joe Manchin of West Virginia.

Irvine’s campaign had planned to file paperwork Monday with the Secretary of State’s office to begin the campaign, according to an email from Indivizement.com, which helped coordinate the effort.

Irvine, who is an ordained minister, is running to replace retiring Sen. Mark Udall in the seat vacated by Democrat Mark Begich, who announced he is seeking the Democratic nomination for president.