Metrolinx is celebrating a milestone in the rollout of credit and debit card tap payment, but the regional transit agency is also acknowledging a problem known as "card clash," where riders are charged multiple times for a single ride.

Since the new way to pay was introduced this past August, more than 100,000 people have tapped their credit cards to pay for GO, Brampton, MiWay and Oakville Transit.

The feature allows passengers to tap on and off of transit using debit and credit cards on Presto card readers, but this new method of contactless payment has come with an unintended consequence.

Riders who keep Presto, credit, and debit cards in the same wallet, purse, or phone — which is kind of the point of having an accessory to carry your cards — might end up double or even triple-charged for their rides when tapping on or off a Presto reader.

Metrolinx states that "the easiest way [to avoid extra charges] is to take out the card they want to pay with out of their wallet, purse or phone case when tapping onto a Presto device to pay. This avoids a situation called 'card clash' and ensures that only one card is charged."

"Customers using their credit card or Presto card should make sure to only tap their preferred payment method onto a Presto device to pay," reads a Metrolinx blog post.

So, essentially, if you want to enjoy the convenience of direct payment without the headache of extra charges, you're forced to inconvenience yourself by fumbling around with cards.

Passengers who choose to go through the trouble of removing cards from their wallets, purses, or phone holders will indeed save money compared to riders paying in cash fare, with credit card and mobile wallet payments counting as discounted Presto fare on GO Transit and UP Express.

Presto remains the only contactless option for TTC passengers, with the local transit agency currently still in the process of exploring contactless options now in use on other transit networks in the region.