City officials said Wednesday they will ask a federal judge for help in preventing unionized police officers from blocking access to the site of the Democratic National Convention (search), where protests have delayed the seven-week, $14 million overhaul.

Labor troubles became more than just an image problem for Democrats when union workers on Tuesday surrounded the FleetCenter, the sports arena that is to be transformed into the convention site by July 26.

Hundreds of firefighters, electricians and other trade workers stood beside unionized police officers, who organized the demonstration to protest their lack of a contract. The union has threatened to maintain a round-the-clock presence outside the FleetCenter and the attached North Station commuter center until Boston Mayor Thomas Menino meets its contract demands.

Merita Hopkins, the city's lawyer, said Wednesday that protesting officers have violated an agreement, reached in federal court last week, that allows for peaceful leafletting in the ongoing contract dispute.

"The expectation was that it was going to be an informational leafleting and that there would be absolute clear and unobstructed ... passage of construction vehicles onto the construction site. This is a matter of respecting the law," Hopkins said.

A hearing is scheduled for Thursday and the city hopes a judge will intervene.

Jim Barry, an official with the police union, denied that protesters have blocked access to the FleetCenter.

Separately, Democratic Party leaders pressed for a quick end to the dispute between Menino and the police union. Sen. Edward Kennedy (search), D-Mass., has made a handful of calls to labor leaders, members of the congressional delegation and the state Democratic Chairman Phil Johnston, according to a Democratic strategist.

Sen. John Kerry (search) of Massachusetts is to be chosen the party's nominee at the convention in his home city.

John Sasso, Kerry's liaison at the Democratic National Committee, also called Jack Corrigan, Kerry's main convention planner, according to a senior DNC official. Democratic National Committee Chairman Terry McAuliffe (search) contacted the mayor on Tuesday, according to Menino spokesman Seth Gitell, who said McAuliffe "just wanted to check in and see what's going on."

Work was slow Wednesday as an angry group of protesting police officers, joined by firefighters and other allies, turned away a crane that was being delivered to the FleetCenter. Only about a dozen union laborers and carpenters reported to work.

"It makes the schedule very, very tough," said Thomas Goemaat, president and chief executive officer of Shawmut Design and Construction, which is the general contractor at the site. "We need resolution."