This one could get interesting. Per USA Today:

Walmart is suing Visa for allowing customers to verify chip-enabled debit card transactions with a signature instead of a PIN.

The lawsuit filed Tuesday in New York Supreme Court says that Visa requires Walmart to accept signature-based transactions for chip debit cards, which Walmart says are a less secure method of payment than PIN-based payments and more expensive to conduct over Visa's network.

"PIN is the only truly secure form of cardholder verification in the marketplace today, and it offers superior security to our customers," says Walmart spokesman Randy Hargrove. "Visa has acknowledged in many other countries that chip-and-pin offer greater security. Visa nevertheless has demanded that we allow fraud-prone signature verification for debit transactions in our U.S. stores because Visa stands to make more money processing those transactions."

And

Walmart automatically prompts customers to enter a PIN when they use a chip debit card, but customers can override it and enter a signature instead. Debit card transactions account for more than 70% of the dollars spent on credit and debit cards at Walmart.

Read the whole thing: Walmart sues Visa over chip transactions with debit cards