William D. Peppers recalled how empty the subway car was. It was not yet 4 a.m. on a Friday, so most of New York was still asleep, but he was already late for his job at a Bronx bakery. As his train passed through Midtown Manhattan, Mr. Peppers stretched out, closed his eyes and nodded off.

Then came the tap. It was a police officer.

Mr. Peppers had put his feet up on a subway seat, and that, the officer informed him, was a crime — one that in his case would lead to his arrest. He spent 12 hours in jail before he saw a judge, and was released after pleading guilty.

“I can see if it was rush hour, but there was no one else on the train. Why not just say, ‘Put your feet down’? ” said Mr. Peppers, a maintenance man at the bakery. “I lost a day of work because of their pettiness.”

It is perhaps the most minor crime New Yorkers are routinely arrested for: sitting improperly on a subway seat. Seven years ago, rule 1050(7)(J) of the city’s transit code criminalized what was once simply bad etiquette: passengers putting their feet on a subway seat. They also cannot take up more than one seat if it interferes with other passengers’ comfort, nor can they block movement on a subway by doing something like standing too close to the doors.