Police confiscated more than two dozen locked-up bicycles last week in Brooklyn, reigniting concern among some activists that the city is illegally seizing private property.

The confiscation of bikes has become a point of legal contention between bicyclists and the city stemming from seizures that have taken place during the monthly Critical Mass bike rides through the city’s streets.

Police said they seized about 25 bicycles in Williamsburg last Wednesday evening after local businesses complained that large clusters of bikes around the Bedford Avenue subway station were impeding sidewalk traffic.

Photographs examined by The New York Sun show police cutting through bike locks using electric circular saws, sending sparks flying and drawing a crowd to the busy intersection of Bedford Avenue and North 7th Street.

The photos show police confiscating bikes locked to the painted, wrought iron guardrails of the station entrance. It is illegal to lock bicycles to property of the Metropolitan Transportation Authority.

The photos also show police cutting the locks of bicycles tied to signposts, a common practice in a city where bicycles outnumber bike racks 35 to one and few office buildings permit people to bring their bike inside. The bicycles in the photos do not appear to be impeding traffic.

A Manhattan federal judge, William Pauley III, ruled last month that the Critical Mass confiscations violated the “due process” clause of the 14th Amendment of the Constitution because police did not provide adequate notice before confiscating bikes locked to signposts.

Word of last week’s confiscations alarmed the lead attorney for the bicyclists, Norman Siegel, who said he thought the recent court decision would prevent mass seizures.

“To seize bikes without adequate notice is an abuse of power and it must stop now,” Mr. Siegel said.

Attorneys for the city were unavailable for comment yesterday.

The city has argued that the practice of locking a bike to a signpost is illegal, a move that has confused riders, who point to a Police Department a brochure urging bicyclists to “lock up your bicycle, even when leaving it ‘for just a few seconds.'” One of the examples the brochure cites of where to lock a bike is a signpost.

Police said the seizures were limited to Williamsburg, where they said the problem of bike congestion is acute.

Legal questions notwithstanding, the act of confiscating 25 bikes and placing them in police vans destined for a Brooklyn warehouse may affect how people park their bikes, at least in Williamsburg.

“People were shocked to see this blatant display of power,” one witness, William Sherman, 20, said. “At one point, the police had to wait before they could cut off any more bikes because the van was full.”

Bicycle activists, who say they have received scores of complaints about police confiscating bicycles, worry that such seizures – and the lack of adequate bicycle parking – will discourage bicycling in the city.

“That’s a sure way to stop people from riding bikes in the city,” the projects director at the advocacy organization Transportation Alternatives, Noah Budnick, said.

To address the issue, a City Council member, Margarita Lopez, introduced a bill this summer that would require police to give at least 36 hours’ notice before confiscating unattended bicycles.