An agreement in principle to end the long-running lockout of St. Paul Chamber Orchestra musicians ran aground Monday, raising doubts about the orchestra’s current season and long-term future.

Negotiators for the musicians’ union rejected the terms brokered last week by St. Paul Mayor Chris Coleman, claiming that SPCO management had failed to include promised changes in the latest proposal, a charge rejected by both Coleman and the orchestra board.

“None of your remaining concerns, in my opinion, rise to the level of importance that would be worth jeopardizing the long-term viability of this orchestra,” Coleman wrote to the musicians Monday.

The SPCO board, which had vowed to cancel the remainder of the season unless a deal was concluded Monday, scheduled a Tuesday meeting to discuss the orchestra’s future.

Agreement had already been reached on the contract’s big-ticket items: a $60,000 minimum salary (an 18.6 percent reduction), an ensemble of 28 musicians, down from 34, a guarantee about overscale pay and a special retirement program.

Coleman entered the negotiations in mid-March. After the first attempt at a deal stalled, he asked musicians to bring him their concerns. He then met with management and last Friday made it clear he felt there was the basis for a deal.

“I believe that all remaining local issues between the SPCO management and the musicians that were prohibiting the resumption of the season are resolved,” the mayor wrote in a letter to the musicians. “I presume you will recommend this new offer to the full membership for approval.”

The musicians’ negotiating team, however, claimed that management’s proposal differed from Coleman’s summary. Among the contentions were disagreements over pay for freelance substitute players and oversight of an artistic review panel. Also unresolved is the relationship between the local deal and a separate agreement with the national American Federation of Musicians on the digital distribution of archived music. This is perhaps the largest sticking point in the negotiations.

Coleman made it clear Monday that he was not persuaded by the union’s arguments.

“I find that their [management’s] proposal meets both their commitment and included everything that I expected,” he wrote. He was not available to comment further.

Minnesota Orchestra

Musicians from the union negotiating team were invited to address a special meeting of the Minnesota Orchestra’s board of directors later this month.

The invitation responds to a long-standing request from the musicians to speak directly to the board about the contract dispute, which resulted in the players being locked out on Oct. 1.

The negotiating team said in a statement that it was considering the invitation.

No date was set.