A police union wants to turn random bystanders into vigilantes-for-hire — by offering $500 to any civilian who helps cops wrestle down suspects who are resisting arrest.

The cash proposal from the Sergeants Benevolent Association is aimed at getting those who normally would make videos of cops taking people into custody to put down their phones and actually get involved.

“When you see an officer struggling, rather than take your cellphone out, assist the officer and you’ll receive an award of $500,” SBA president Ed Mullins told The Post.

“Far too often, we see police officers engaged in violent struggles with perpetrators while members of the public stand by and take videos of the incident. This has got to stop, and hopefully this program will incentivize good Samaritans to do the right thing.”

State Sen. Martin Golden (R-Brooklyn), a retired cop, will introduce a new good Samaritan law to shield civilians from liability if they help cops. The bill is still being drafted, his office said.

“The current good Samaritan law does not protect citizens who assist first responders. It is my intent to introduce legislation in the Senate that corrects this shortcoming,” Golden said.

An existing law covers those who give medical aid to an ailing person without expectation of reward.

The union will pay for rewards, but its officials hope pro-cop groups and private individuals will pitch in. They didn’t give many details about what would constitute enough help to warrant a reward, although the union noted that grabbing and holding a suspect whom the cops are chasing would qualify.

They said a panel of experts would rule on whether any assistance merited a payout.

A police spokesperson said, “The NYPD encourages people to support their cops by calling 911. The department doesn’t want to see people put in harm’s way unnecessarily to collect a reward.”

Some cops support the union plan.

“I love that idea,” said a police source. “Now you’re actually going to have people out there trying to help stop crimes.”

But others thought it could just raise new problems.

“Why not just appeal to people to help a cop. Why do you have to pay them?” said a high-ranking police source. “The good Samaritans will turn around and sue the city because they got hurt.”

Civil liberties groups took a dim view of the initiative.

“In the era of Trump and the Alt-Right, incentivizing the public with $500 to ‘assist’ an officer with an arrest, only encourages vigilantism and continues to promote lawlessness within an already unaccountable police department,” said the social justice group El Grito de Sunset Park.