Thousands of Carleton University students are being punished for sneaking a weekly necessity — laundry.

Students at the Ottawa university figured out a way to cheat the machines in the campus laundry room.

All students pay for laundry by swiping their student card at the room's payment machine, then punching in the number of the laundry machine they used.

But some students discovered if they told the payment machine they used one specific machine, you wouldn't get billed due to a computer glitch. Soon, every student who knew about the trick only ever "used" that machine, but were washing clothes in whatever machine was available.

"It was fun, it was just cheap," said James Salmon, a second-year student who used the trick every week.

"As a student you just gotta kind of go for the cheapest route. And if that comes down to kind of screwing the laundry machine for free laundry machine services … then of course why wouldn't you, right?"

Wrong, said Carleton University earlier this week after clueing in to the scam. It's making students who used the trick pay back the money they should have spent on laundry — a bill of $186 for Salmon.

Students found a way to trick this card swiping machine. (CBC)

Ed Kane, Carleton's assistant vice-president of university services, said students should have come clean and pointed out the glitch sooner.

"No one volunteered the information, so essentially we've had to go back," Kane said.

"It's unfortunate they didn't, because we've really had to go back and retroactively bill them and bill their cards directly for the charges."

Kane said the university is owed around $28,000.

Students upset with repayments

While some students are sad a fun trick that saved them a few bucks is gone, others are furious with the university's decision to nail them with an unforeseen fee. They say if they can’t have the fee dropped, they’d prefer to be billed so they can pay at a later date.

"Students are now in negative debt on their campus cards," said George Parry, with the Rideau River residence association.

"Now they can't pay laundry again, or even buy anything from Tim Hortons or the convenience store."

The university said it will not waive the debt, but if students are in a dire financial situation the housing office will consider transferring their debt to their tuition to pay at a later date.