Internet companies including Amazon.com, Google, Netflix and Microsoft in a letter said they oppose a U.S. regulator’s call for allowing companies to pay for fast lanes on the Internet.

The companies said the rules may let phone and cable providers “discriminate both technically and financially against Internet companies” and “impose new tolls on them.”

Federal Communications Commission (FCC) Chairman Tom Wheeler has proposed letting service providers such as AT&T and Comcast negotiate deals with content makers for quicker and more reliable delivery of their video and other fare.

Wheeler has said the idea doesn’t abandon the FCC’s Internet fairness policy, commonly known as “net neutrality.” His proposal is set for an initial vote at the FCC on May 15. “This represents a grave threat to the Internet,” the companies said in the letter addressed to Wheeler and the four other FCC commissioners.

The FCC should protect users and Internet companies against blocking of Web traffic, discrimination and paid prioritization, the companies said.

A court in January threw out FCC rules designed to ensure Web traffic is handled fairly, and the agency is seeking new rules. The vote next week will commence a comment period, and Wheeler has said he wants a final decision this year.

Advocacy groups including Public Knowledge and Free Press that have supported rules to prevent Internet-service providers from unfairly blocking or slowing Web traffic said payment arrangements won’t protect Internet users.

FCC Commissioner Jessica Rosenworcel, who like Wheeler is part of the agency’s Democratic majority, Wednesday called for a delay of the vote “by at least a month.”

“I have real concerns about FCC Chairman Wheeler’s proposal on network neutrality,” Rosenworcel said. The plan has unleashed “a torrent” of reaction and “rushing headlong into a rule making next week fails to respect the public response,” she said.

Companies signing the letter included Amazon; Netflix, the biggest online-video-subscription service; and Microsoft. Also listed as signing were eBay, the top online marketplace; Yahoo, the largest U.S. Web portal; and the Twitter messaging service.