The Republican National Convention (search) is more than three weeks away but an unlikely group of demonstrators has already turned up to protest: off-duty police officers and firefighters agitating for a new labor contract.

One officer outside Madison Square Garden (search) held a sign that read: "Low pay + fewer cops + terrorism = formula for disaster."

The demonstration last month was another reminder that a bitter labor dispute involving public safety unions could further cloud a convention already consumed by security concerns.

Delegates will arrive amid new warnings that terrorists have plotted to strike the New York Stock Exchange (search) and other sites in Manhattan. But union officials say the heightened alert hasn't discouraged plans for off-duty protests.

"There's a lot of unhappy firefighters out there," said Stephen Cassidy, president of the Uniformed Firefighters Association.

At the Democratic National Convention (search) in Boston, last-minute contract settlements averted protests by police and firefighter unions. Much of the rhetoric — laced with references to the Sept. 11, 2001, terrorist attacks — suggests there's little hope for a similar deal.

Cassidy dismissed the city's offer of a 5 percent wage increase over three years to police and firefighters as "an insult to the heroes of Sept. 11."

Bloomberg also has taken a hard line, insisting the city can't afford a higher raise and accusing union officers of "trying to intimidate the city."

"Yelling and screaming is just counterproductive," he said.

Union members plan to skip a massive organized labor rally outside the convention on Sept. 1 protesting President Bush's economic policies. Instead, their strategy calls for "informational picketing" by off-duty officers and firefighters at delegation gatherings in other locations, particularly if the mayor is a guest.

"We're not interested in protesting against the president," Cassidy said. "We want to make sure people know that Mike Bloomberg doesn't give a damn."

The bad blood predates the convention by more than two years: Police have been working without a contract since July 31, 2002, and firefighters since May 31, 2002. The situation fits a pattern of retroactive contracts and negotiations that routinely ignore expiration dates and end in arbitration.

With contract talks stalled, the Patrolmen's Benevolent Association spent $75,000 on a flashy Times Square billboard in January to demand better pay. It claimed that the city's officers — who earn $34,500 to $60,300 a year — are ranked 145th in pay among the nation's police departments.

The unions' latest volley came last week when a truck bearing a "Billionaire Bloomberg" billboard circled a Staten Island news conference at which the wealthy mayor was announcing funds for a new park.

Bloomberg brushed it off, saying, "They spelled my name right, and I appreciate the advertising."