Comcast Corp., the biggest cable and second-largest internet service provider in the United States, says the Federal Communications Commission has come knocking about complaints the company actively interferes with its subscribers' internet traffic.

Consumer groups and technology companies have accused Comcast of discriminating against certain types of internet traffic, such as the peer-to-peer software behind applications including BitTorrent — which is popular among file sharers — and Skype. 

A California resident in November lodged a lawsuit against the company for blocking certain kinds of tracking, followed shortly by a complaint to the FCC by Vuze, a video distributor that uses BitTorrent. The company asked the regulator to spell out just how much power ISPs have in controlling traffic on their networks.

FCC chairman Kevin Martin on Jan. 9 told reporters that the regulator would investigate the claims. The FCC has given Comcast until Jan. 25 to respond in writing to accusations that it blocks internet traffic. The regulator also opened up a public comment period on the issue.

Comcast, which has previously said it manages traffic in order to provide better connectivity to all customers, on Monday said it is not running afoul of any regulations. It has also denied it blocks file sharing, despite a test in October by the Associated Press that found the contrary.

"We look forward to responding to the FCC inquiries regarding our broadband network management," said David Cohen, an executive vice-president at Comcast, in a statement. "We believe our practices are in accordance with the FCC's policy statement on the internet where the commission clearly recognized that reasonable network management is necessary for the good of all customers."

A number of Canadian ISPs, including Rogers Communications Inc. and Bell Canada Inc., have also admitted to traffic shaping, but have denied blocking peer-to-peer applications.

The issue of "traffic shaping," where an ISP manages bandwidth to ensure that certain applications work well, is becoming central to arguments for legislated net neutrality. Critics of traffic shaping say ISPs should not be allowed to decide which internet applications get better speeds, as this can lead to discrimination against certain types of services, thus infringing on consumers' rights and limiting innovation.

The potential for some sort of government-mandated net neutrality laws has spooked investors in companies that make traffic-shaping tools. Waterloo, Ont.-based Sandvine Corp. established itself as a market darling last year, with shares in the company rising from around $2 at the beginning of the year to more than $7 in October.

However, since the lawsuit and complaints have focused attention on traffic-shaping practices by ISPs, Sandvine shares have plummeted to around $4. Shares of the company were down more than three per cent in mid-day trading on the Toronto Stock Exchange on Tuesday, to $4.06.