MADISON, Wis. — State Sen. Dale Schultz, a former Republican Senate majority leader who has broken with his party on major issues in recent years, will face a primary challenger should he seek re-election in 2014.

In a sign of how deep the anger at Schultz runs among Republicans, state Rep. Howard Marklein announced over the weekend that he would be running for the Senate seat covering southwest Wisconsin. The August 2014 primary is 16 months away.

Schultz, of Richland Center, is part of an 18-15 Republican majority in the Senate. He has represented southwestern Wisconsin, first in the Assembly and then in the Senate, since 1983. Marklein, of Spring Green, joined the Assembly in 2010.

While Schultz twice served as the leader of Senate Republicans, most recently in 2006, he drew the ire of party faithful when he voted against Gov. Scott Walker’s bill in 2011 that effectively ended collective bargaining for most public workers.

Wisconsin Democratic Party Chairman Mike Tate invited Schultz to become a Democrat on Monday, saying it’s the only way he can win re-election. Schultz laughed off that offer, saying he’s been a Republican for 45 years and has no intention of changing.

“My fierce independence on issues that affect my constituents has been appreciated over the years,” Schultz said. “Everybody knows I want to work with everybody to meet the challenges this state faces.”

Marklein said he better represents the district, in part because he voted for two of the highest profile issues to come before the Legislature in recent years, both of which Schultz opposed.

Schultz was the only Republican in either the Senate or Assembly to vote against the collective bargaining measure, which was such a partisan issue that it drove Senate Democrats from the state in a futile attempt to block the bill and spurred a series of recalls against lawmakers and Walker.

This year, Schultz was also the lone Republican to vote against a bill that eased the state’s environmental regulations to help speed the opening of an iron ore mine near Lake Superior.

“I believe I represented my district well,” Marklein said. “I took those votes last session and I was re-elected.”

Schultz said he wouldn’t make up his mind on whether to seek a seventh term in the Senate until early next year. He said Marklein’s decision to run against him was unexpected but not a surprise.

“After 30 years in the state Legislature, nothing surprises me anymore,” Schultz said. He said he thought he could stave off a primary challenge because he voted with Republicans 98.7 percent of the time.

Marklein, an accountant, won both of his elections in 2010 and 2012 by margins of 52 percent to 48 percent. He serves as chairman of the Assembly’s Ways and Means Committee and vice chair of the Assembly Audit Committee.

On his campaign website, Marklein mentioned that he supported the mining bill and that he would focus on efforts to improve the economy and bring the same budgeting standards to state government that private companies use.

Democrats have been eyeing Schultz’s district as a place where they could gain ground in the Senate. Marklein’s decision to get into the race only fueled that talk.

“This is a real game changer in the Senate,” said Scott Spector, executive director of Wisconsin Progress, an advocacy group that tries to get liberal Democrats elected.

“Dale Schultz is the only Republican who had a chance to win this seat in November and now he has to defend himself in a Republican primary where tea party special interests are bound to bankroll Marklein’s campaign,” Spector said in an email.

Schultz said he expected outside groups to flood his district should he run against Marklein.

“I’m aware that there’s a tea party element out there that wants to push the political process to the right and I think you’re going to see this play out nationally,” he said. “This is not just about Dale Schultz. I’m a microcosm of a much larger fight.”