ST. PAUL, Minn. — Republican state Sen. Dave Thompson opened his campaign for Minnesota governor Wednesday with promises to seek voucher-like tax credits to enhance school choice, to pursue a law that would diminish union clout and to otherwise reduce the presence of government in people's lives.

"As your governor, my goal will be to get out of your way," Thompson pledged at the outset of a campaign swing.

He's the fourth Republican in the race, with others still mulling a challenge against Democratic Gov. Mark Dayton next year. With an ardently conservative background and a tea-party-tinged message, Thompson's presence in the race could tug the GOP's nomination contest more to the right. The office is the top target of Minnesota Republicans, who haven't won a statewide election since 2006.

In elected office for just three years, Thompson hasn't shied from the spotlight. He was one of the most vocal opponents of state assistance to build a new Minnesota Vikings stadium and he riled labor unions with a proposed constitutional amendment that would have made union membership voluntary in Minnesota. The right-to-work measure stalled even though fellow Republicans ran both legislative chambers at the time.

Thompson, 51, said it would be wrong to classify him as anti-union, but said union leadership has become too powerful and detached from rank-and-file priorities. Either way, union officials made clear they would aggressively confront him in a gubernatorial campaign.

Within minutes of Thompson's inaugural news conference, Minnesota AFL-CIO President Shar Knutson warned Thompson would "bring Scott Walker-style politics to Minnesota," referring to the Wisconsin governor who unleashed a firestorm with his moves to weaken organized labor.

As governor, Thompson said he would sign a right-to-work law, although the presence of a Democratic Senate makes the prospect unlikely in the short term. On education, he said would try to enact tax credits that give money to parents from struggling schools, particularly in urban areas, to send their children to private schools. He said he wouldn't attempt to undo Minnesota's new gay marriage law because "frankly, the people have spoken."

Thompson has been married to his wife Rhonda for 28 years and has a son and a daughter. He was raised by a single mother, and said his upbringing helps him relate to average Minnesotans.

He is banking on support from Republican activists who will endorse a candidate at next spring's state convention. He said he would end his campaign without that nod even though some rivals are vowing to continue to the August 2014 primary no matter what.

Thompson, who grew up in greater Minnesota but now lives in suburban Lakeville, built a following as a conservative talk radio show host. Thompson acknowledged the shows could provide opponents campaign fodder, but he said they won't find a trove of edgy comments.

"I really said the same stuff on talk radio that I say now. There's a reason for that: I believe it," he said. "I wasn't a shock guy. I tried to call it like I saw it."

His KSTP-AM show was cancelled in 2009 after a nearly eight-year run. He went on to consult for the state GOP in the 2010 election and won a Senate seat that year. He was quickly elevated into the leadership ranks of the new majority caucus.

Thompson may face competition from fellow Sen. David Hann, the current minority leader who is considering a run. Three Republicans already in the race are former House Speaker Kurt Zellers, businessman Scott Honour and Hennepin County Commissioner Jeff Johnson.

Former state GOP executive director Ben Zierke, who isn't aligned in the race, said he doesn't see wide differences in ideology among the four announced candidates. Zierke said the candidates will rise or fall based on the forward-looking vision and plans they project.

"You can't run for the next 14 or 15 months on 'We are not Mark Dayton.' People know that," Zierke said. "It's how are you different than Mark Dayton? That's how the separation will come."

Dayton has never run for re-election to an office he has held, serving single terms as auditor and U.S. senator. He said he doesn't intend to fully engage in the campaign until a clear Republican nominee emerges, but he's busy raising money after having self-financed most of his prior campaigns.

"I know there will be a blizzard of attacks against me, starting really soon," Dayton said Tuesday. "I'm going to raise every dollar I legally can so I can respond."