Picketing police officers marched to City Hall from the site of the Democratic National Convention (search) on Friday after federal marshals began monitoring whether they were impeding efforts to convert the sports arena into a staging ground for John Kerry's (search) nomination.

Several hundred officers — chanting "contracts now!" and "Tommy" — paraded toward City Hall, their uniformed, on-duty brethren stopping traffic along the way to let them through the streets. When they arrived at city hall plaza, some of them sat at a table set up outside, sending a message that they wanted to continue contract talks with Mayor Thomas M. Menino (search).

Moments later, several hundred officers walked into City Hall, where they held an impromptu rally in the city council chambers for about five minutes, vowing to not back down in their fight to reach a contract agreement with the city. Menino was not in the building at the time.

Protesters peacefully dispersed after the rally, and union officials said there were no immediate plans for continued picketing.

Five vehicles entered the convention site around 10:30 a.m., the first large showing of construction workers since the $14 million renovation project was to have begun earlier in the week.

Boston police have been working without a contract for about two years, and Menino has been under increasing pressure to reach a deal with the union. Democratic leaders are concerned that picketing police officers or a show of force by other disgruntled unionized workers will hamper plans for the city to host its first-ever national political convention.

The end to the police demonstrations came a day after U.S. District Judge Joseph L. Tauro warned pickets led by the Boston Police Patrolmen's Association (search) to stop blocking people or vehicles from entering the job site at the FleetCenter (search). Five U.S. marshals sent by Tauro to observe whether pickets followed his orders patrolled the site Friday.

Work at the FleetCenter was supposed to start Tuesday, but the police union and its allies surrounded workers and trucks that have tried to enter the site, shouting at them to "go home" and physically standing in their way. Most turned away. The union denied that its actions amounted to unlawful intimidation, and Tauro said he would not tolerate it.

The picket line had dwindled in numbers and receded to the edges of the entrances. Police association president Thomas J. Nee said union leaders would meet over the weekend and reorganize.

"I don't need no stinkin' marshals in my town," Nee said. "We have been denied our constitutional rights by a federal judge."

The construction work, including installing phone lines and removing arena seats to accommodate a large stage, will prepare the arena for the convention July 26-29. A tour for news media scheduled for Tuesday has been postponed until June 29.