Metrolinx says approximately 1,100 preloaded Presto cards have been stolen from a third-party vendor.
It says the cards, valued at $20 each, were taken on Dec. 27.
Metrolinx says it has determined that none of the cards were in use as of Friday and the cards have been blocked and will have no value.
Spokeswoman Anne Marie Aikins says Metrolinx is working with the vendor and Toronto police to investigate the theft.
Aikins says Metrolinx is reminding customers to beware of any offers of Presto cards from sources other than authorized retailers.