Hennepin County administrators withheld critical salary information during a contract arbitration with a group of ranking sheriff deputies, a move that will now cost the county more than $300,000, an arbitrator ruled.

A ruling released last week said Todd Olness, the county's labor relations representative, didn't disclose that a group of majors and the chief deputy in the Sheriff's Office received 7.5 percent raises. During contract negotiations with the office's 61 other supervisors, Olness stressed that the county's philosophy was to distribute uniform pay adjustments and benefits across all bargaining units, the ruling said.

The supervisors, which includes sergeants, lieutenants and captains, settled for a 2.5 percent raise over the course of a contract from 2016 through this year. Olness predicted that to award the licensed supervisors "even a dollar's worth of extra pay without compelling justification to do so would be disastrous," the ruling said.

Arbitrator Richard J. Miller wrote that labor relations are built on trust and honesty between the parties and not on omission or failure to provide relevant information, which happened in this case.

"This is very disappointing," he wrote. "It's a logical conclusion that the county did not want the union or the arbitrator to have this substantial evidence that negated their policy that all county employees were being treated the same."

The county cannot appeal the binding arbitration. But Mark Thompson, the county's assistant administrator of public safety, denied the county withheld any salary information. The higher raises for managers in the Sheriff's Office were awarded after the union-represented supervisors had already agreed to their pay increase, he said.

"It would be bad for morale if we handled raises for managers before the rank and file," he said.

Last week's arbitration ruling has been more than two years in the making. The county and the union started collective bargaining in late 2015 when its contract expired. They were unable to reach an agreement and went to arbitration in July 2017.

Before the hearing, the attorney for the supervisors, Kimberly Sobieck, made a 19-point data request with the county's labor relations department. In response, Olness provided all the information — except the salary raise for the majors and chief deputy, the arbitrator found.

"The county had a legal duty to respond," she said. "They had the info, and we needed it." Sobieck said it was the county administration, not Sheriff Rich Stanek, that made those decisions.

Olness said the omission was inadvertent and unintentional, the ruling said. He did apologize to Sobieck and the heads of the union, and as a gesture of goodwill, Thompson agreed to have Miller hold another arbitration hearing. The county wasn't obligated to do it, Thompson said.

The next hearing was held in March, and the union asked for an additional 5 percent raise to reach the 7.5 percent given to the majors and chief deputy. The county objected.

In his April 2 ruling, Miller agreed to the 5 percent pay raise because data showed the licensed supervisors were paid less than supervisors in other metro counties. The average additional pay works out to nearly $5,000 per supervisor.