With their publication in the Federal Register, the FCC's controversial net neutrality rules are now official—and open to legal challenges.

Though the commission approved the rules in February, they are not truly on the books until their publication in the Federal Register. They appeared there this morning, and will formally go into effect on June 12, the document said.

It's a procedural move, but noteworthy because it means lawsuits can now be filed against the rules.

Indeed, USTelecom, which made its intentions known last month, formally filed suit today in the U.S. Court of Appeals for D.C., arguing that the commission had no authority to pass its rules.

According to USTelecom President Walter McCormick, the rules are an "unjustifiable shift backward to common carrier regulation after more than a decade of significantly expanded broadband access and services for consumers under light-touch regulation."

The rules re-classified broadband as a telecom service rather than an information service in order to give the FCC more legal authority to regulate ISPs. The agency went that route after its previous rules, passed in 2010, were challenged by Verizon, which ultimately succeeded in court and had them struck down.

Publicly, the ISPs argue that they adhere to net neutrality rules on their own, and do not need the FCC to interfere. The agency, however, says rules of the road provide a means for consumers to complain should their ISPs engage in nefarious activity. The whole debate, in fact, dates back to accusations that Comcast blocked access to P2P sites like BitTorrent in order to speed up its own network.

Congress is considering a bill that would strip the FCC of its authority to re-classify broadband, among other things, but it has not yet seen any significant action.

Matt Wood, policy director of Free Press, which supports the rules, said today that "publication of the rules brings us one step closer to having the enforceable Net Neutrality protections that millions of Americans have called for."

"While Internet service providers will spend buckets of money to woo Congress and file lawsuits, people everywhere will continue fighting for the open Internet protections they won," Wood said.