American Express has blocked attempts by Curve to load Amex cards into its all-in-one wallet, just days after the UK startup announced support for the feature.
The addition of Amex support would allow Curve customers to spend with Amex anywhere Mastercard is accepted for the first time, solving the annoyance card members have of retailers not accepting Amex cards due to their high fees.
Curve has been trialling Amex compatibility with its platform in closed Beta since November. During this time, at least 500 Curve users spent more than £1 million on their Amex cards, the company says.
In blocking the feature, Amex says it is not obliged to work with any third parties or individual merchants and that it terminated support for "business reasons".
This explanation has cut no ice with Curve, which is vowing to fight Amex's decision and take its case to the relevant regulatory bodies.
"Amex has given no good or fair reason for their decision and we believe it is entirely disproportionate and discriminatory to Curve and all our (joint) customers," says the firm in a statement to customers. "UK payment regulations clearly state that Curve should be allowed to access the Amex payment network on a level-playing field with every other fee-paying and legitimate merchant."
In a later bog post, Curve goes even further: "We intend to challenge Amex's decision. We have already sent a letter to them to reconsider their decision and have given them reasonable time to comply. Failure to do so will mean that we will be forced to exercise our rights in the courts and to submit complaints to the relevant regulators in the UK and Europe."