Visa filed a suit against Walmart June 30, the latest volley in a legal shootout with large retailers over EMV, chip-and-PIN and signature policies. “To me, it’s a clear escalation in the battle,” said Rick Oglesby, president of AZ Payments Group and a partner at Double Diamond Group. “It’s never a good thing to be wrapped up in a public dispute with one of your largest and most influential customers, and the networks versus Walmart has been ongoing for many years.”

The suit claims Walmart surreptitiously tested a process in which shoppers were not given the choice to verify their Visa debit card purchases with a signature. It’s the most recent salvo in a battle among Visa and large retailers over the use of either signatures or PINs to verify transactions.

Walmart sued Visa in May, alleging the card brand demanded signature verification for debit transactions even though PIN is more secure.

In mid June, Walmart Canada said it would begin in mid July to refuse to accept Visa due to high transaction fees; Home Depot went after Visa and MasterCard in court in mid-June with chip-and-PIN/signature complaints at the heart of the suit; and grocery giant Kroger filed suit against Visa June 27 because it says Visa changed its mind too many times regarding EMV migration process and hardware.

According to Reuters, Visa detected a decrease in debit card transactions after Walmart’s “PIN-only policy” was secretly instituted and got complaints from customers when they couldn’t use debit cards at Walmart without a PIN. The combatants traded different versions of the proceedings, of course.

Oglesby said observers should get used to the nastiness.

“Walmart taking a very hard line in Canada, the MCX partnership with Chase, the courts negating the interchange settlement, and Walmart’s suit regarding debit routing are all indications that the battle is heating up, and that Walmart is going for blood,” Oglesby said.

“Visa’s response is likely necessary from a legal standpoint, at the same time it’s bringing about an ugly public escalation of a persistent battle that actually has a foundation in the network business model. It’s hard to see this ending any time soon.”