The CEOs of Visa, Mastercard, PayPal Holdings and Stripe received letters Thursday from Federal Trade Commission Chair Andrew Ferguson, who demanded they not discriminate against customers based on political or religious grounds.

The FTC threatened enforcement action if customers are denied services for those reasons.

Any act to “deplatform customers or deny them access to financial products or services” may violate the Federal Trade Commission Act and “could lead to an FTC investigation and potential enforcement action,” the agency said in a Thursday press release. The FTC didn’t cite any specific infractions by the companies.

The commission is typically made up of five members, but has just two at the moment. President Donald Trump last fired two of the Democrats who sat on the commission.