BISMARCK, N.D. — North Dakota congressional candidate Tom Campbell, a wealthy potato farmer, is paying registration fees for some delegates to attend the state party’s convention next month.

Campbell’s main Republican rival for the state’s lone House seat, state Sen. Kelly Armstrong, and North Dakota vice chairman Jim Poolman said party rules do not forbid the practice. However, they said the rare move smacks of vote-buying in an attempt to get delegates’ endorsement to run against Mac Schneider, who was chosen Saturday as the state Democrats’ favored candidate.

Campaign spokesman Mike Schrimpf said Campbell, a state senator from Grafton, has paid registration costs for an undisclosed number of delegates to “encourage participation” at the convention “for folks where the expense of registration could be a barrier.”

Schrimpf said Campbell “is definitely not paying for non-registration costs,” such as hotels and other expenses. He would not say how much Campbell has spent or will spend.

Registration fees for the convention to be held April 6-8 in Grand Forks are $90 per person, or $45 for those under 30 years old. The convention is expected to draw more than 1,200 delegates, Poolman said. He said delegates must a written report to the party if they receive any compensation from a candidate or their campaign, though the requirement relies mostly on the honor system.

Several delegates and lawmakers have voiced complaints to the party about Campbell doling out money, Poolman said. He said the party required the written reports after similar allegations several years ago that never were proven.

Delegates at the GOP state convention will pick their endorsement to run for the state’s lone congressional seat being left open by Congressman Kevin Cramer who last month launched his campaign for U.S. Senate, where he is hoping to unseat Democratic Sen. Heidi Heitkamp in what is expected to be one of the toughest Senate races in the U.S.

The House contest will be the GOP convention’s featured race, with Campbell, Armstrong and Marine veteran Tiffany Abentroth competing for the endorsement. Frequent candidate DuWayne Hendrickson and Paul Schaffner, who is appealing a recent prostitution solicitation conviction, also have announced their candidacies but have no realistic chance of getting the party nod.

Abentroth did not return telephone calls seeking comment.

Armstrong, who is a lawyer and oil company executive, said he said he covered registration costs for his parents, and his brother and sister-in-law, all of whom are delegates.

“I did pay for delegate fees for my mom and dad — mostly because I didn’t trust them to go on the computer and figure out how to do it,” Armstrong said. He said his brother and sister-in-law are reimbursing him for the fees.

Armstrong, who stepped down as the GOP party chairman after announcing his House bid, said he won’t be funding any other costs for delegates at the convention.

“I’m not doing it because it feels like you’re buying a vote,” he said. “What (Campbell’s campaign) is doing is up to them.”

Campbell has dug deep into his own pocket for the past several months to buy TV ads to raise his profile statewide. About three-quarters of the more than $1 million he has raised has come from himself, Federal Election Commission filings show.

A convention endorsement only guarantees a candidate a spot on the June 12 primary ballot and party support against any challengers. Campbell has signaled he will continue on to the primary if he does not get his party’s endorsement.

Armstrong said in just three weeks he has raised more than $500,000, which includes $100,000 of his own money.