Failing to pay a parking ticket from a privately owned lot could get you slapped with a fine higher than the parking rate and threaten your credit rating.

That happened to one Calgary woman, who received a letter from a collections agency demanding $100 for a $30 ticket she says she never got. The letter told her to pay up or it may go on her credit report.

"I don't remember getting a ticket. I did not get a reminder notice. I did not get a phone call saying, ‘Hey, if you don't pay this, we'll send this to a credit agency,'" said Liza Mulholland.

The ticket was written by Precise ParkLink in April. The lot has since been taken over by Calgary's largest parking company, Impark.

CTV Calgary's consumer specialist Lea Williams-Doherty contacted Precise ParkLink president Gord White, who refused to talk about Mulholland's ticket in particular even though Mulholland had given written consent to do so. But White agreed to discuss his company's policies over the phone.

Williams-Doherty asked under what authority is Precise ParkLink charging customers who don't pay tickets on time three times the posted rate.

White said it's because customers agree to a contract with Precise ParkLink, a contract that is posted on signs in the parking lot.

And it turns out, the law backs this up.

"If an individual goes on a lot, they're entering into a contract and as a government, I don't inferfere with that," said Service Alberta Minister Heather Klimchuk.

A Court of Appeals decision against Impark established the rule that if lot operators post clear signage that indicates it is offering to enter into a contract and provides the terms, customers who leave their cars in the lot are deemed to have agreed to that contract. Customers are obliged to pay additional penalties for unpaid parking tickets.

In the past, people who had unpaid tickets were required to pay only the amount that should have been paid on the parking date. And if those customers parked on that company's lots in the future and still had outstanding tickets, the company had the right to tow their vehicles.

Mulholland thought she only had to pay what she owed the day she parked, not the penalty, and she didn't think an unpaid private parking ticket could ruin her credit.

"Everyone works hard to protect their credit rating and now mine's perhaps in jeopardy. It's ridiculous," she said.

White said that when people don't pay tickets it becomes an unpaid contractual debt, which companies can send to collection agencies without notice. He also said his company makes no attempt to contact people in arrears and that accounts go straight to collections, which is legal.

Whether or not you get follow-up notices for overdue "invoices" in the mail, get referred to a collections agency, or get towed depends entirely on which company is running the lot.

Collection agencies often threaten to put a black mark on your credit report. But that almost never happens.