State lawmakers and a mayor were among those expected Friday to lead a packed field of nearly two dozen contenders for the Utah congressional seat soon to be vacated by U.S. Rep. Jason Chaffetz.

Fifteen Republicans, four Democrats, one Libertarian and two independents have filed to run after Chaffetz announced he would step down next month from the heavily Republican 3rd Congressional District, which stretches from suburban Salt Lake City to desert towns in southeastern Utah.

Friday is the final day to file to run for most candidates.

Republican state Sen. Deidre Henderson could be a key candidate. She has served in the state Senate since 2013 and was Chaffetz's campaign manager in his run for office in 2008.

John Curtis, mayor of the city of Provo, which is home to the Mormon-owned Brigham Young University, could also get some traction. Despite name recognition and a track record as a popular mayor, he may struggle to gain enough support at his party's convention after previously running as a Democrat before becoming a Republican in 2006.

Curtis, a moderate-leaning Republican, said his biggest policy issues include pushing for smarter spending, protecting Utah's monuments and strengthening Americans' trust in law enforcement.

Boyd Matheson, a veteran Utah Republican strategist, predicts that Henderson and Curtis would be key contenders, along with GOP Sen. Margaret Dayton, who has served in the Senate since 2006, and Chris Herrod, a loan officer in Provo who had been a Republican state representative for five years beginning in 2007.

But other candidates also could do well, Matheson said, including GOP Rep. Brad Daw and Republican Tanner Ainge, son of Boston Celtics President Danny Ainge.

The packed field of candidates has a lot to do with the election lacking an incumbent, said Matheson, who runs the conservative Sutherland Institute.

"The fact that this is an open seat really opens the gates for people who wouldn't go up and challenge an incumbent per se," he said.

A small handful of Democrats also have jumped in to the race, with Dr. Kathryn Allen expected to be the party's front-runner. But they are expected to face an uphill battle given the district's deeply conservative leanings.

The Republican and Democratic parties were expected to narrow their candidate fields at separate conventions on June 17 before a Nov. 7 special election.