Verizon Communications sent a cease and desist letter to Netflix, threatening to sue if Netflix doesn’t stop displaying messages to customers that blame slow streaming speeds on Verizon’s Internet service, Reuters reports.

As previously reported, a war of words flared up after Netflix began blaming Verizon for slow streams, with Verizon saying in a statement that Netflix wasn’t being straight with its customers.

“The letter is the latest sign of tension between content providers like Netflix and Internet service providers over who should pay the price for companies that stream heavy traffic online,” the Reuters report notes.

Verizon’s letter demanded that Netflix provide it with a list of customers to whom Netflix had sent the notices. “Failure to provide this information may lead us to pursue legal remedies," Verizon general counsel Randal Milch said in a letter to Netflix general counsel David Hyman.