Comcast has appealed last month’s FCC ruling that it improperly blocked Internet file-sharing activities.

The cable company, which filed suit Thursday in the U.S. District Court of Appeals in Washington, called the August decision “legally inappropriate,” because the agency had not previously established any rules about this activity. The FCC based its 3-2 decision on net neutrality principles intended to protect Internet users’ rights.

The FCC ruled that Comcast activities were “discriminatory and arbitrary,” and noted that the type of video file-sharing activity Comcast has been blocking reps a competitive threat to cable operators.

The FCC weighed in on Comcast’s practices after users complained that the company was blocking downloads of large data files, usually video. It was later discovered that the company was cutting off transfers without informing customers. Comcast has said that it was delaying traffic, not blocking it, in order to prevent high bandwidth users from slowing other customers’ Internet activities.

The FCC action did not include a fine but requires the company to submit a compliance plan describing how it intends to stop these practices by the end of the year. The company said it will comply with the FCC’s order, but said it filed the appeal “to challenge the basis on which the Commission has found that Comcast violated federal policy.”

FCC chair Kevin Martin has argued that Internet usage is so rapidly evolving that it makes more regulatory sense to rely on broad principles rather than established rules.

Last week, a public interest law firm representing two consumer groups and a California company that benefits from the type of file-sharing software targeted by Comcast filed appeals in New York, Philadelphia and San Francisco.

Media Access Project in Washington is repping plaintiffs Consumers Union, in Yonkers, N.Y.; PennPIRG in Philadelphia; and Vuze Inc. of Redwood City, Calif. They are asking the court to force Comcast to cease its management practices immediately rather than by the end of the year.

Since the FCC vote, Comcast has announced that beginning Oct. 1, it would institute a broadband usage cap of 250 gigabytes per month for all residential customers. Comcast says to exceed that limit a customer would have to send 50 million emails or download 125 standard-definition movies.

(The Associated Press contributed to this report.)