Angry city teachers who refused to be bullied by their union posted Facebook photos on Thursday of themselves in NYPD T-shirts — after the UFT warned them not to wear the “inappropriate apparel” on the first day of classes.

Many teachers had worn the shirts to school Tuesday and Wednesday as a show of support for cops in the wake of the Eric Garner death and union-backed rally by the Rev. Al Sharpton.

But they were warned by a United Federation of Teachers official in an email late Wednesday that, “as public employees, one must remain objective at all times. Certain T-shirt messages may appear to be supportive, but individuals (parents, students) may see a different meaning in that message.”

The memo also raised the specter of “potential implications” career-wise, noting: “Principals may report any inappropriate apparel to the chancellor.”

A Staten Island teaching assistant told The Post she got a phone call directly from her principal Wednesday night “telling me not to wear the shirt, as per the UFT.”

The threatening messages scared many teachers from wearing their shirts on Thursday.

But a handful of teachers defied the warning, most notably at IS 72 on Staten Island — which is named after slain cop Rocco Laurie, sources said.

Other teachers across the city posted photos of themselves in pro-cop attire on a Facebook page titled “Thank you, NYPD.”

One picture, shot Wednesday, shows 20 teachers at PS 220 in Queens gathered in a classroom while wearing gray NYPD shirts supplied by a teacher whose boyfriend is a city cop.

“We didn’t agree with [the UFT’s] backing the Al Sharpton thing,” one comment read.

Another photo shows more than 40 teachers wearing specially designed white T’s bearing a heart-shaped image of a handshake and the words “New York’s Brightest Supports New York’s Finest.”

Cindi Panarella, the UFT chapter leader at PS 44 in Mariners Harbor, called the union’s action “crazy.”

“The UFT contract specifically says there is no dress code. They can’t tell us what to wear,” she said.

Ed Mullins, president of the Sergeants Benevolent Association, said he was proud of the shirt-wearing teachers “for having the courage to stand up for something they believe in.”

He said UFT chief Michael Mulgrew “is a hypocrite because he marched in Staten Island and he claimed the UFT had a history of being activists. Now he has teachers who are being activists themselves by wearing a T-shirt, and he doesn’t agree with them.”

During an appearance on Governor’s Island, Mulgrew said, “Everybody has a right to voice their opinion.”

A spokesman for the DOE said, “Anything that distracts or disrupts learning should be left out of school buildings.”

Additional reporting by Joe Tacopino, Reuven Fenton, Aaron Short, Shawn Cohen and Amber Sutherland