That was historically the case, but allowing merchants to offer cash discounts is protected under U.S. federal law since 2010: https://en.wikipedia.org/wiki/Durbin_amendment. Around me, only gas stations and liquor stores seem to commonly offer such discounts though.

What's less settled is whether businesses can charge credit-card customers a CC surcharge to pass on the fees. Economic theory would consider this functionally the same as offering a cash discount, but it differs in calling out the CC fee as a line item charge. Some state laws prohibit that, and they've been tied up in litigation, e.g. this mostly inconclusive 2017 Supreme Court ruling that kicked the question back down to lower courts: https://www.scotusblog.com/2017/03/opinion-analysis-justices...