The FCC has found that Comcast's internet monitoring is like reading people's mail. (Douglas C. Pizac/Associated Press)

Comcast Corp., the largest U.S. cable provider, has been chastised by U.S. regulators for interfering with its customers' internet access and ordered to stop the practice.

The Federal Communications Commission on Wednesday handed down an order that said Comcast had violated the core principles of providing internet access by slowing and blocking customers use of peer-to-peer applications such as BitTorrent, which is used to transfer large files.

In a 67-page decision, the FCC said Comcast had "misleadingly disclaimed any responsibility for the customers' [bandwidth] problems" and deliberately changed its story several times after being caught in the act of throttling access. The regulator also found that throttling was happening at all times of day, rather than only at peak periods as Comcast had claimed, and that up to 75 per cent of customers may have been affected.

"This practice is not 'minimally intrusive' but invasive and outright discriminatory," the FCC said in its ruling. "Consumers are entitled to run applications and use services of their choice."

The regulator has given the company 30 days to disclose its network management practices and come up with a plan as to how it will provide internet access in a non-discriminatory way. Although the ruling was only against Comcast, the FCC warned other service providers that it will not tolerate throttling of certain uses of the internet.

"Should [the FCC] see evidence that providers of telecommunications for internet access or IP-enabled services are violating principles, we will not hesitate to take action to address that conduct," the ruling said.

The FCC's investigation of Comcast mirrors a similar probe of internet throttling by Bell Canada Inc. by the Canadian Radio-television and Telecommunications Commission. Bell is also throttling customers' access to peer-to-peer applications and, like Comcast, the company said it is only doing so during peak hours of the day.

The CRTC is scheduled to rule by the end of October as to whether Bell has violated the Telecommunications Act by extending the throttling practices to its smaller wholesale customers, such as TekSavvy and Acanac, who are members of the Canadian Association of Internet Providers. The regulator has said it will likely launch another probe into throttling by internet service providers in general.

In its ruling, the FCC echoed a charge levelled by CAIP in its complaint that Bell's monitoring of internet traffic is like reading people's mail. The U.S. regulator found that Comcast's throttling was like opening "its customers' mail because it wants to deliver mail not based on the address or type of stamp on the envelope but on the type of letter contained therein."

Comcast has indicated it plans to instead target heavy downloaders for throttling, rather than specific internet uses.