New York City buses will be back door-only starting Monday in a bid to prevent the spread of coronavirus, the MTA and its bus operator unions announced Friday.

Riders who do not have mobility disabilities will be required to enter buses on local and “Select Bus Service” routes through the rear door, according to the new policy.

On local routes, riders will no longer enter near the farebox, which is right next to the driver’s seat — effectively eliminating fare collection on those routes, an MTA source said.

Fare collection will continue on Select Bus Service and express routes.

On express charter buses, which carry riders between the far edges of the city and its Manhattan core, riders will be required to sit at least three rows behind the driver.

“This is the right move,” Transport Workers Local 100 President Tony Utano said in a statement. “It will better protect our bus operators, give them some peace of mind, and demonstrate that their concerns have been heard.”

Bus ridership has plummeted as a result of the outbreak — but at a lesser rate than on subways and commuter rails, whose riders tend to be relatively higher income.

The announcement of the new policy comes the day after the MTA confirmed employees out of the Fresh Pond bus depot had tested positive for the COVID-19 virus.

As of Thursday evening, the MTA had confirmed 23 positive coronavirus cases among its 74,000-person workforce.