Visa and MasterCard said they can no longer support their payment cards being used in Crimea.
The move by the world’s biggest payment card companies follows the latest round of US sanctions imposed earlier this month over Russia’s annexation of the peninsula in March.
The United States has prohibited US-registered companies from investing in Crimea or providing services to firms operating there.
Many cardholders have experienced declined transactions in shops and at cash machines.
Meanwhile trains between Ukraine and Crimea are being suspended because of unspecified “security concerns”.
Ukraine’s state rail company said cargo services have already stopped. Passenger services will gradually cease between now and Monday.
“In order to ensure the safety of passengers … [the railway] will cut the route of trains to Crimea off at Novooleksiyvka and Kherson,” it said in a statement, referring to two towns on the Ukrainian mainland near Crimea.