Merchants in a Bainbridge Avenue building that sustained significant damage in a fire last Halloween are locked in a legal battle with their landlord who is suing each of them for tens of thousands of dollars in back rent.

The owners of the businesses — Betty’s Place hair salon, Ming Wong Chinese restaurant, a laundromat and a 99-cent store — say the landlord is unfairly seeking back rent during a months-long period following the fire when they couldn’t operate their businesses.

Already, a Bronx housing court judge ruled in favor of the landlord, saying the business owners failed to notify the landlord in writing that they could not operate their businesses because gas had not been restored to the building following the fire, according to lawyers representing the business owners.

The judge is now handing out penalties in each case individually — one of the merchants was ordered to pay more than $20,000 and another more than $18,000. A lawyer for the merchants said the judge has yet to assess penalties in another case, while the fourth case was scheduled for October 20.

Susan Chase, a lawyer for the Legal Aid Society which is working with the merchants, said, “The gist is, they didn’t have gas, they couldn’t operate their businesses.”

Skadden, a big multi-national law firm, has assigned two lawyers to help Chase appeal the decisions. “It’s a tough situation for everybody,” said Thomas Claps, who’s working on the case for Skadden.

On Tuesday, Claps said he was optimistic about the appeal, saying there is precedent in New York in cases where landlords had knowledge of events that caused their tenants to shut down their businesses. In those cases, he said, the tenants were not deemed liable for back rent.

David Rosenbaum, a lawyer for the landlord, did not return calls seeking comment.

Last Friday, Betty (she declined to give her last name) who owns Betty’s Place hair salon was shaving the head of a young customer.

Because of the time off and faulty electricity, which prevents her from taking on extra hair dressers, she said business is “horrible.” Even if the judgment against her is overturned, she said she still might leave. “Really, with all the headache, I don’t want to stay anymore.”