The move follows action by the U.S. Federal Communications Commission earlier this month in which the FCC criticized and banned Comcast's practice of throttling back BitTorrent peer-to-peer traffic in an effort to manage and reduce network congestion. The FCC's decision was seen as an attempt to prevent violations of so-called net neutrality principles that ensure uninterrupted Internet traffic.

Comcast, however, said its new policy has been in the making for many months. "It's no secret we've been evaluating a specific monthly data usage or bandwidth threshold for our Comcast High-Speed Internet residential customers for some time," Comcast said Thursday in a statement on its Website about its new guidelines of Comcast's Acceptable Use Policy. "We've listened to feedback from our customers who asked that we provide a specific threshold for data usage and this would help them understand the amount of usage that would qualify as excessive."

Comcast said that once the plan goes into effect, the company will contact customers who go over the limit and ask them to curb their usage.

"This is the same system we have in place today," Comcast said. "The only difference is that we will now provide a limit by which a customer may be contacted. As part of our pre-existing policy, we will continue to contact the top users of our high-speed Internet service and ask them to curb their usage. If a customer uses more than 250 GB and is one of the top users of our service, he or she may be contacted by Comcast to notify them of excessive use. At that time, we'll tell them exactly how much data per month they had used. We know from experience the vast majority of customers we ask to curb usage do so voluntarily."

The nation's second-largest Internet service provider said that the median monthly data use by residential customers is 2 GB to 3 GB, so the new threshold should not represent a significant hindrance in most cases.

Comcast said that to use 250 GBs of data, a customer would have to do one of the following: send 50 million emails at 0.05 KB per email; download 62,500 songs at 4 MB per song; download 125 standard-definition movies at 2 GB per movie; or upload 25,000 hi-resolution digital photos at 10 MB per photo.

However, Comcast's policy does not address issues involved with rapidly-growing, Web-based storage services that such as those provided by Mozy, which is owned by EMC and which offers online data backup.

Other ISPs have in place or are testing caps, according to the Associated Press. Cox Communications has monthly caps that vary from 5 GB to 75 GB. Time Warner Cable is testing caps between 5 GB and 40 GB in one market. The telephone company Frontier Communications plans to charge extra for use of more than 5 GB per month, the AP said.