Boston Mayor Thomas Menino (search) is urging delegates to next week's Democratic National Convention not to be deterred by picket lines by city police officers unhappy about working without a labor contract.

In the letter sent over the weekend, Menino said the pickets are informational and not an official strike line.

Police have promised to picket next Sunday at each of the 29 delegation welcome parties, as well as at other events Menino attends for the July 26-29 convention.

"It's a right they have, but it shouldn't stop anyone from coming to the convention and having a good time, especially at the delegation parties," Menino said in an interview Sunday.

Menino, the official host of each of the welcome parties, sent his letter a week after the Boston Police Patrolmen's Association (search) sent delegates a missive of their own. The union's letter asked delegates to respect their picket lines and to boycott the parties, along with the mayor's address to the convention at the FleetCenter.

"It's very shortsighted by anybody to take that letter they got from the patrolmen's association at face value," Menino said Sunday. "It was a self-serving letter."

Union officials derided Menino's attempt to depict their effort as something less than an official picket line.

"This is a picket line — it's an economic picket line," said Jim Barry, the association's legislative agent. "What does Menino know about a picket line anyway? He's never walked one."

The 1,400-member police union has been without a contract for just over two years. The union is demanding a 17 percent pay increase over four years, while Menino has offered 11.9 percent.

Police picket lines temporarily halted construction at the convention site last month and deterred hometown son and Democratic presidential candidate John Kerry from addressing the U.S. Mayors Conference in Boston, which Menino hosted.

Leaders of at least six state delegations have said they will not cross picket lines to attend the official welcome parties. Menino says that will only harm the small businesses hired to put on the parties.