A year after Costco and American Express announced their split, the warehouse club said Thursday that June 19 will be the last day that it will accept American Express credit cards.

Details were disclosed on Costco.com and in the warehouses, where shoppers were given slips of paper at the checkouts explaining the change.

The partnership has been in effect for 16 years and it is a sizable one for both firms.

Ten percent of American Express cards are co-branded with Costco. Experts believe that talks broke down when Costco wanted lower fees. "These are high-stakes negotiations," said Jason Steele, credit card expert at Comparecards.com. "Costco wants the lowest possible merchant fees."

Last month, Citigroup announced it would buy the Costco credit card portfolio from American Express.

Starting June 20, Costco will accept any Visa card, not just the Citibank Visa, as well as cash, checks, and debit cards, but not American Express.

According to Costco.com, American Express cardholders will continue to earn cash back rewards on all eligible purchases through June 19, which will automatically transfer to the new card from Citibank. The reward check for both cards will be enclosed in the February 2017 Citi bill.

After June 19, the Costco American Express cards will not be valid anywhere.

Steele believes it is unlikely that American Express will automatically mail its former cardholders non-Costco affiliated AmEx cards. When Northwest Airlines and Delta merged, card holders with a Northwest travel reward program didn't automatically get a Delta-affiliated credit card.

Costco AmEx cardholders do not need to apply for the new credit card. Citibank Visa will automatically be sending a new card to members in May or June. Information regarding the accounts will be sent out in April, according to Costco.

Perks on the new Costco Anywhere card are even better than with AmEx. Cardholders will now get a 4 percent cash back on gas purchases worldwide up to $7,000. The old benefit was 3 percent. Restaurant and travel expenses will get a 3 percent benefit, Costco purchases get 2 percent, and everything else gets 1 percent.

"Consumers are getting better deals with greater rewards," Steele said. The Citi Double Cash card offers a 2 percent reward instead of the more common one percent on most purchases and some credit cards are now offering six points per dollar spent instead of two.

In Minnesota, Costco has six locations in the Twin Cities, one in Rochester and one in Baxter.

John Ewoldt • 612-673-7633