A “bus rider town hall” hosted by Mayor Zohran Mamdani crossed a “deeply concerning line” by allowing the city’s Democratic Socialists of America chapter to have a table at the government-run meeting in Brooklyn, experts said Friday.

The NYC-DSA’s dedicated kiosk during Thursday night’s event for bus riders at the Brooklyn College Conference Center raised concerns among good-government groups and critics about City Hall mixing politics and civic engagement.

“There needs to be a bright line between government-led civic engagement and political organizing,” Citizens Union Executive Director Grace Rauh told The Post.

“A government-run town hall that crosses that line is deeply concerning,” she said.

The head of the government watchdog group called on the Mamdani administration to explain why the far-left political organization — which the mayor is a member of — was allowed to take part in the town hall.

“The public needs an explanation from City Hall about how a partisan political organization was able to set up a table at an official city event, and what steps will be taken to ensure there is a bright line between partisan activity and government-run civic engagement going forward,” she said.

The mayor arrived at the event at about 7 p.m., sitting down in front of a cardboard cutout of a bus as Councilwoman Rita Joseph asked him and three “bus riders” questions about what bus rides mean to them.

The riders included a member from the PSC CUNY and SEIU 1199 unions each and an advocate for the non-profit Riders Alliance transportation advocacy group. About 100 other participants were also present.

Mamdani delivered a short speech at the end, telling the crowd he was excited to bring the city’s first “Bus Rapid Transit Route” to Flatbush Avenue. The mayor unveiled the project last month alongside Gov. Kathy Hochul, and it is said to be completed in 2030.

“It will go so fast that it won’t just be those who have no other option that are riding the bus, it’ll be those who’ll want to get where they’re going,” he said.

City Councilwoman Joann Ariola, a Queens Republican, railed that allowing DSA to be involved in the event was “dystopian.”

“The DSA is looking to turn every city event, even something as mundane as a town hall, into a political rally,” she fumed to The Post. “This kind of rampant party glorification is what you’d expect to see from a totalitarian dictator, not in the streets of NYC.”

City Hall didn’t answer questions about the DSA’s involvement, including whether the administration had sought any ethics guidance or whether any registration information or attendee contact information was shared with the political group.

“The Central Brooklyn Town Hall brought together bus riders from across the borough. For the town hall, a number of community and advocacy organizations that work on transit issues were invited to table, including Fair Fares NYC, Transportation Alternatives, the DSA’s transit working group and Riders Alliance,” said Senior Mayoral Spokeswoman Dora Pekec. 

Some attendees complained that the city and state’s plan for faster buses — the B103 route change first pitched in 2022 and continued under Mamdani’s administration as part of its “Next Stop” transit initiative — could ultimately make their commutes longer.

Cynthia Clarke, a 76-year-old retired nurse, and her friend Juanita Jordan, 72, a retired legal secretary, said they were scared to lose their B103 bus stop from their neighborhood in Kensington.

“We would have to take two and three buses just to get to where we want to go — and that’s unfair,” Clarke said.

Jordan said transit officials dismissed her concerns.

“We were hoping that they would tell us that this is really not going to happen,” Jordan said.

“But they said that there’s going to be more meetings addressing that situation… I wrote this on a piece of paper, where they said we should write down our main concern. But they said that this was not the issue tonight.”

Charles D’Souza, the founder of transit advocacy group Passengers United said that many of the staffers at the event seemed “clueless” about the local issues.

“They just seemed clueless. They were just standing in the corner, playing with their phones,” he told The Post.

“They meant well. They were smiling and they were listening, but I felt like they were not educated on the routes and the particular community.”

The DSA did not respond to requests for comment.