Visa, the payments company, has terminated its relationship with WaveCrest, a cryptocurrency card provider.

Citing an email from WaveCrest, CNBC reported the company said it has been forced to close all Visa cards, which left thousands of people with declined transactions and worries about how to access their money.

"As a licensed E-Money Institution, WaveCrest is required to safeguard funds to cover all of its issued electronic money, and we can confirm that these funds are safe and available for redemption through other channels," the company said in the statement.

Meanwhile, Visa told CNBC that it terminated its relationship with a single prepaid card issuer in Europe for violating Visa's operating regulations. “That issuer, WaveCrest, was required to close its Visa card products, some of which were linked to cryptocurrency wallets," the statement said.

Dmitry Lazarichev, co-founder of cryptocurrency card operator Wirex, said he has fielded thousands of calls from concerned customers since Visa’s move. The executive said that Wirex has issued around 500,000 cryptocurrency debit cards around the globe, but not inside the U.S.

"All the cards were shut down in one second," Lazarichev said, adding that WaveCrest hasn't been responsive. "We asked for more information, but they haven't provided any."

Visa noted in its statement to CNBC that they are not specifically targeting cryptocurrency, and that the move reflects the card issuer’s “failure to comply with Visa's policies that ensure the safety and integrity of our payment system."

In November, news surfaced that Singapore residents will soon be able to make purchases with a prepaid Visa card backed by the cryptocurrency platform Monaco. Both iOS and Android users in Singapore will be able to download the Monaco app and select one of five available Visa prepaid card options, including the Monaco Visa Platinum. They must then complete a three-minute onboarding process to get on the waiting list. It's not clear if that will change with Visa's most recent move.