The Justice Department on Thursday threw its two cents into the ongoing debate over "Net neutrality," telling the FCC it opposes regulating Internet traffic.

Net neutrality is the principle that all data on the Internet should be treated equally.

For instance, a huge, three-gigabyte movie download is currently given the same priority as a 10-kilobyte e-mail as it wends from router to router on its way to the consumer.

Telephone and cable companies, who own most of the "last mile" infrastructure that connects American homes and businesses to the backbone of the Internet, want to be allowed to charge Web-based companies a premium to provide faster downloads for bigger files.

That could heavily affect those firms whose Web offerings take up a lot of bandwidth.

YouTube, Apple Inc. and Movielink are obvious examples, but many other companies are beginning to offer music and video online, such as Amazon, MTV, and even FOXNews.com's parent company, News Corporation, which is launching a video Web site with NBC Universal.

The telecoms, led by AT&T Inc., Verizon Communications Inc. and Comcast Corp., argue that high-volume uploaders should pay for part of the cost of upgrading last-mile connections. The higher price would guarantee a speedier connection.

"Last mile" owners say that Net-neutrality legislation, various forms of which have been bouncing around Congress for the past couple of years, would kill any incentives for replacing older copper cables with newer, more efficient fiber-optic lines.

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The DOJ took the telecoms' point of view in its filing, saying that Net-neutrality regulation could hamper development of the Internet and could shift the "entire burden of implementing costly network expansions and improvements onto consumers."

The agency said providing different levels of service is common, efficient and could satisfy consumers.

As an example, it cited the U.S. Postal Service, which charges customers different guarantees and speeds for package delivery, ranging from bulk mail to overnight delivery.

"Whether or not the same type of differentiated products and services will develop on the Internet should be determined by market forces, not regulatory intervention," DOJ said.

It added that regulation could have "significant negative effects for the economy and consumers."

Advocates of Net neutrality cite a different analogy: They point out that telephone service always has been user-neutral, and that even telegraph companies in the 19th century were mandated by the government to not favor one transmission over another.

In late June, Federal Trade Commission Chairwoman Deborah Platt Majoras also came out against Net-neutrality regulation, saying that without evidence of "market failure or demonstrated consumer harm, policy makers should be particularly hesitant to enact new regulation in this area."

The Web industry, as might be expected, is mostly in favor of legislation mandating Net neutrality, arguing that failure to do so would stifle innovation and competition.

Google co-founder Sergey Brin testified before Congress in favor of Net neutrality last year. Some tech experts believe Google, which owns YouTube, is secretly building its own nationwide high-speed network in case the legislation fails.

Consumers probably would not initially be forced to pay more under premium upload pricing, but would notice that files downloaded from companies that do pay the higher fees will arrive faster than files from those that don't.

But it would also mean that start-up companies, such as YouTube was 18 months ago, could be strangled at birth by the extra costs.

The Associated Press contributed to this report.