SAN FRANCISCO (KRON) — Global supply chain issues have severely depleted the inventory of plastic Clipper cards, according to a press release from BART and the Metropolitan Transportation Commission (MTC). The transit agencies are encouraging travelers to switch from the plastic cards to the Clipper card app for mobile devices.

Through the end of the year, the agencies will be waiving the standard $3 new card fee for customers who opt for the mobile app option, rather than the plastic card. Customers who opt for the traditional plastic card will still be charged the $3, according to the release.

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BART, which is the largest vendor of the cards, has installed signs near ticket vending machines letting travelers know they can save $3 by putting the app on their phones, rather than buying a card. Ticket vending machines at the San Francisco International Airport station, meanwhile, are temporarily dispensing old-style paper tickets.

Clipper is available for mobile phone through either Apple Pay or Google Pay. The shortage of plastic Clipper cards is expected to last for several months.