A Manhattan condo board president was so adamant about illegally renting out his luxury Chelsea loft to tourists that he twice had a neighbor who tried to block the practice falsely arrested, a new lawsuit alleges.

Interior designer Jonathan Baron, 54, filed a $1 million defamation suit against the allegedly haughty hotelier in Manhattan Supreme Court, saying he trashed his reputation, The Post has learned.

Seven Black, 43, a trainer at David Barton Gym, allegedly rents out one of his two pads at 315 Seventh Ave., a 550-square-foot studio, Baron discovered.

He showed The Post a copy of a Web page from the Cyber Rentals site advertising a Chelsea loft studio for $250 a night. The listing says, “Call Seven.”

“I have a laundry room across the hall from my apartment and it was being used by strangers that I did not know as residents in my building,” Baron told The Post. “I found out from the strangers that they were renting a unit in the building on a weekly basis.”

Black’s attorney, Bryan Mazzola, said his client “does not run an illegal hotel.”

“We feel that the allegations are frivolous,” Mazzola said. “At the end of the day, we believe we have a strong case and we’ll be able to have this thing dismissed.”

After Baron confronted Black, the board president had him arrested for menacing and criminal weapons possession in August 2011, records show.

The charges were dismissed. But Baron said he lost a job at the Fashion Institute of Technology because human resources tracked down the incident during a background check.