Some straphangers who tapped their way into the subway system Monday morning were greeted with sticker shock: rather than getting charged the standard $2.75 to board the train, they discovered they had been docked $2.90.

Earlier this month, the MTA's board voted to approve fare and toll hikes that will see the base fare for subway, local bus, Staten Island Railway and paratransit rides rise from $2.75 to $2.90, but that change is only set to take effect on Aug. 20.

In a statement provided to NY1, MTA spokesperson Aaron Donovan attributed Monday morning’s accidental fare increase to Cubic, the vendor building out the agency’s contactless payment system, known as OMNY.

Donovan said the company “prematurely” rolled out software changes that were meant to kick in on Aug. 20.

“The MTA immediately directed Cubic to rectify the problem, which was resolved at approximately 9 a.m.,” Donovan said. “Anyone who was charged $2.90 will be reimbursed 15 cents per transaction. The MTA thanks our customers for bringing this to our attention quickly and apologizes for the inconvenience.”

MTA customers who used their MetroCards Monday morning were not overcharged, the agency said. It wasn’t immediately clear how many riders were overcharged due to the error, or how riders would receive their refunds.

In a statement provided to NY1 on Tuesday, Cubic said the premature fare hike happened "during system testing of the new fare structure slated to take effect" on Aug. 20. 

"This issue was immediately addressed by the Cubic Transportation Systems team and refunds of the incorrectly charged fares have been returned to customer accounts," Cubic said in the statement. "We sincerely apologize for any inconvenience that this caused riders who rely on the OMNY system for their travels throughout the New York City metro area. We will be taking steps to address the cause of the error and prevent such an incident in the future.”