Ontario’s finance department says roughly 6,500 used car buyers are on the hook for sales tax they weren’t charged when they purchased used vehicles in May, 2015.

The provincial government is attributing the error to CarProof providing lower values than was reasonable for the affected vehicles. CarProof is a private contractor the government hired to assign resale values to used vehicles. Cars sold in May were mistakenly undervalued, and buyers were consequently not charged enough tax; most of the bills being sent to those used car buyers are for between $100 and $500, adding up to a total of $2.4 million in outstanding sales tax.

Ontario Finance Minister Charles Sousa called the mistake “unfortunate,” adding that the government has no choice but to collect the funds, even though the car buyers did nothing wrong. He didn’t say what it would cost to send bills to the affected car buyers.

“I acknowledge and regret that an isolated situation has unfortunately occurred due to a computer formatting error with third party data,” Sousa told the Toronto Star. “(It) has resulted in certain people being required to pay an outstanding balance of RST owing on their recent used car purchases, (but) I want to reiterate that this is an isolated incident and the ministry has taken appropriate steps to ensure that this does not happen again.”

Ontario NDP leader Andrea Horwath suggested the Liberals “need to do a better job of keeping their eye on what the government and its private-sector service providers are doing. They farm out (these initiatives), don’t keep tabs on them, and something ends up going awry.”

Used vehicle buyers who receive a bill for outstanding sales tax can mail a cheque or money order to the Ministry of Finance, or pay in person at Ontario’s ServiceOntario locations.