(AP) PROVIDENCE, R.I.

About 100 Providence firefighters have begun their picket of the U.S. Conference of Mayors' 77th annual meeting.

Members of the firefighters union, locked in a contract dispute with Providence Mayor David Cicilline (sis-ah-LEEN'-ee), held signs that said "Cicilline (equals) DemoRat" and wore T-shirts that said "Fire Cicilline."

Vice President Joseph Biden was supposed to attend the conference starting Friday but canceled last week after the firefighters said they would picket.

Union president Paul Doughty (DOW'-tee) says Cicilline has trampled on their first amendment rights by requiring protesters to register and stand across the street.

Cicilline said the tactics of the firefighters have dampened Providence's chances of shining on a national stage and called the protest "political extortion."

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