A police officer was taken off patrol duty Monday after being caught on video knocking a cyclist to the ground during a protest in Times Square.

The video was taken by a tourist on Friday night and posted on YouTube.com.

It shows the officer approaching and then pushing the cyclist during the monthly Critical Mass ride, which protests automobile usage.

Prosecutors say the cyclist, Christopher Long, was charged with blocking traffic, resisting arrest, disorderly conduct and assault.

In court papers, the arresting officer claims the biker was disrupting traffic — and when he tried to get the biker to stop, the biker turned at him and knocked him to the ground. The police are not commenting about the officer's account.

Critical Mass says this is the second time in 16 months a peaceful demonstrator has been thrown off his bike by police.

"I was not surprised at all. I've seen a lot of this kind of thing,” said Bill DiPaola, director of Time’s Up. “I was happy that the public came off the street and was upset that the police did this so we are seeing more interaction from the general public."

"I think the police department needs to look into this very quickly and very thoroughly and assure bicycle riders that they will be safe on New York City streets," said Democratic Brooklyn Councilman David Yassky.

The arresting officer, Patrick Pogan, will remain on modified duty pending an NYPD investigation.