But Verizon, Comcast and others trace the video problems to the way that Netflix has chosen to deliver some of its content through intermediaries, a theory that Netflix ridiculed again Monday.
Blaming Netflix for the network congestion "is like blaming drivers on a bridge for traffic jams when you're the one who decided to leave three lanes closed during rush hour," Netflix general counsel David Hyman wrote in a Monday letter to his counterpart at Verizon. He said that Verizon had misinterpreted Netflix's efforts to inform subscribers when an Internet service's network is becoming clogged.
New York-based Verizon Communications Inc. declined to comment Monday. In a June 5 letter, Verizon had threatened to sue Netflix Inc. unless the company stopped sending messages that made Verizon's Internet service look bad. Verizon had given Netflix until Tuesday to provide proof of its derogatory claims about Verizon's service.
The notices are part of a "small-scale test" that will end June 16, according to a Monday post on Netflix's blog. The test lasted about a month and spanned a "few hundred thousand" customers, said Netflix spokesman Joris Evers. About 36 million U.S. subscribers pay $8 to $12 per month for the service.
Netflix may send unflattering messages across an even bigger swath of subscribers if video-quality problems persist.
The Los Gatos, California, company struck deals earlier this year to connect directly into the networks of Verizon and Comcast for an undisclosed amount. Those partnerships haven't placated Netflix, which is trying to convince government regulators that it and other online services shouldn't be forced to pay Internet providers to ensure their content reaches Web surfers.
Since the company agreed to work with Comcast, Netflix's video has been streaming at higher speeds, according to Netflix's own monthly breakdowns. Netflix said its video transmitted at an average of 2.72 megabits per second in May, up 80 percent from January, before the traffic deal.
But Netflix said that the average streaming speed of its video on Verizon's FIOS service declined slightly from April to May, the first month that the companies worked together.