SEATTLE — Costco’s switch from American Express to Visa is being pushed back to this summer.

Costco Wholesale had previously announced that the switch in the only credit card it will accept in its U.S. stores would happen in April.

It’s now saying that transition will happen in June or by mid-summer.

For years, Amex had been the Seattle-area retail giant’s credit card network and the issuer of its co-branded credit cards.

But last year, Costco said it had struck a deal with Visa to replace Amex as its credit-card network, and for Citigroup to become the exclusive issuer of its co-branded credit cards. The co-branded cards also act as Costco membership cards and come with a rewards program.

The original contract with Amex ends March 31 this year, but “our plan is to extend that” by a few months until the Citigroup deal kicks in, said Richard Galanti, Costco’s chief financial officer.