WASHINGTON – Two senators on Friday called for a congressional hearing to investigate reports that phone and cable companies are unfairly stifling communications over the Internet and on cell phones.

Sens. Byron Dorgan, D-N.D., and Olympia Snowe, R-Maine, said the incidents involving several companies, including Comcast Corp., Verizon Wireless and AT&T Inc., have raised serious concerns over the companies’ “power to discriminate against content.”

They want the Senate Commerce, Science and Transportation Committee to investigate whether such incidents were based on legitimate business policies or unfair and anticompetitive practices and if more federal regulation is needed.

“The phone and cable companies have previously stated that they would never use their market power to operate as content gatekeepers and have called efforts to put rules in place to protect consumers ‘a solution in search of a problem,”‘ they said in a letter to Sen. Daniel Inouye, D-Hawaii, the committee’s chairman.

A committee spokeswoman declined to comment on the matter.

An Associated Press report on Oct. 19 detailed how Comcast Corp. was interfering with file-sharing by some of its Internet subscribers. The AP found instances in some areas of the country where traffic was blocked or delayed significantly.

Comcast – the nation’s No. 2 Internet provider – has acknowledged “delaying” some subscriber Internet data, but said the delays are temporary and intended to improve surfing for other users.

Verizon Wireless in late September denied a request by Naral Pro-Choice America, an abortion rights group, to use its mobile network for a sign-up text messaging program.

The company reversed course just a day later, calling it a mistake and an “isolated incident.”

AT&T reportedly changed a service agreement that previously included language permitting the company to cancel accounts of Internet users who disparage the company.

Several lawmakers, including Dorgan, earlier this year introduced legislation promoting “Net neutrality,” which is the principle that all Internet traffic be treated equally by carriers.