Cop-hating radicals wreaked havoc on New York City’s subways on Friday — vandalizing turnstiles, station walls and buses to protest a police crackdown on turnstile jumping.

The agitators — who want police completely out of the subways and transit to be free — secured emergency gates open with bike locks, zip-ties and violin strings, rendered turnstiles useless with glue and spray paint and littered buses, stations and trains with ““F–k cops, f–k MTA,” “Free transit ” and other anti-cop, anti-MTA messages.

“We encourage you to link up with your friends, your family and think of the ways you can move in affinity to f–k s–t up on J-31 all day long,” a masked man said in a video posted to the Twitter page of “Decolonize This Place,” the group organizing the demonstrations, ahead of the day of protests.

The goals of the group include “no cops in the MTA, free transit [and] no harassment,” according to the video.

Protests began early Friday morning. Walls and display screens at the Upper West Side’s 72nd Street B and C train station were marred with graffiti Friday around 7 a.m., cops said.

Just before 8 a.m., protesters strung a large black banner with the words, “F–k your $2.75. Fare strike today,” from the Oculus at the World Trade Center station, according to a video posted by the group. People could be heard clapping and cheering as the banner was unfurled.

Photos obtained by The Post also show anti-cop graffiti at the 155th Street C station. Police received reports of graffiti — as well as glue lining the MetroCard strips — at the 115th Street A/C station, the 145th Street A/C station, the 155th Street C train station, the 96th Street B/C station and Borough Hall station in Brooklyn, authorities said.

Meanwhile, Metro-North officials warned of dangerous rush-hour crowds at Grand Central Terminal as cop-hating radicals wreaked havoc on New York City’s subways ahead of a 5 p.m. “citywide convergence” at the transit hub.

“Customers in the vicinity of Grand Central Terminal may experience increased crowding and street closures due to potential demonstrations,” the commuter railroad said in a statement posted to Twitter.

“Please plan extra travel time or consider taking one of our Friday early getaway trains.”

The protests are a “true endgame of the anti-police movement, an end of all policing & destruction of public order,” the Police Benevolent Association said.

“Our members have spent their careers — and in some cases given their lives — to bring public safety back to NYC,” the union tweeted. “We can’t go backwards.”

The NYPD “is aware of the demonstration and will have an adequate police presence in place,” a department spokeswoman said.

The protests come as MTA and NYPD increase the presence of cops on subways and buses to combat fare evasion, sex crimes and attacks on transit workers.

MTA spokesman Tim Minton said it will be a costly clean-up.

“Some of the tactics that have been discussed threatened to put both riders and employees at risk for their safety,” Minton told The Post.

Police had no immediate word Friday afternoon on protest-related arrests.

Additional reporting by Tina Moore