Philadelphia’s chief executive had a lien placed on his home after failing to pay his gas bill for months.

Mayor Michael Nutter owed $507.76 to the Philadelphia Gas Works (PGW) for service delivered to his home in the Wynnefield section of the city, according to a court documents.

The lien was filed on May 18 in Pennsylvania’s Court of Common Pleas – Civil Division.

Mayor Nutter responded Thursday to questions about the lien saying he "literally just missed" the bill.

"I thought that I had taken care of a particular bill, apparently I had not," he said. "I've been a consistent regular customer and payer to PGW and made a mistake."

PGW Director of Corporate Communications Barry O’Sullivan couldn’t speak specifically about Mayor Nutter’s case citing customer privacy, but said the utility’s lien issuance is automated.

“You would have to be at least $300 behind in your bill for 90 days or more,” O’Sullivan said.

O’Sullivan said once that threshold is met, a pre-lien letter is sent to the customer alerting them to the impending legal action. The customer has an additional 60 days before the lien is placed. During that period, two additional letters are sent out – one 10 days prior and another three days prior to the court filing.

“The process of placing liens is put in place to allow us to recoup money for natural gas we’ve already delivered,” O’Sullivan said. He said service shutoff is separate and is used to prevent chronically behind customers from continuing to receive service for free.

NBC10 obtained a copy of the final, three day notice sent to Mayor Nutter. Dated May 3, the notice warned that service may be shut off if the debt was not settled immediately.

Mayor Nutter said all citizens have an obligation to "pay what we owe."

PGW serves more than 480,000 residential customers and nearly 20,000 commercial customers in the city. O’Sullivan says at any given time, up to a third of those customers are late at paying their bills for a variety of reasons.

Approximately 4,000 liens were levied in May to all customers over past due PGW bills, according to O'Sullivan. He says that's higher than average because the utility has a self-imposed moratorium on service stoppage during the cold weather months -- stretching from November to March. PGW then begins to ramp up collections of deliquent bills once those months have passed.

City Controller Alan Butkovitz criticized the late payment saying the mayor needs to lead by example.