The move comes as Aereo, which recently won a major appeals court ruling on nearly the same issue in New York, prepares to offer its service in Boston and 22 other markets as soon as this month. CBS and other broadcasters have vowed to sue to stop Aereo in those new markets, a threat that appears to have led it to file the new court action. (The new filing, reported by AllThingsD, refers to recent public statements and Twitter feeds by CBS executives, including one that says “we’ll sue”).

So what exactly is the meaning of Aereo’s new lawsuit? Here’s what one copyright expert familiar with the issue had to say:

Aereo’s decision to file a separate declaratory judgment action at this stage is unorthodox. They’ve prevailed on a preliminary injunction motion at the district and circuit court level — which means that both the Southern District and the 2d Circuit have ruled they are likely to succeed on the merits — so it’s unusual to seek a declaratory judgment on the same issues.

Recall that the appeals court decision from last month already protects Aereo for the immediate future in the U.S. Second District, a territory that covers the states of New York, Vermont and Connecticut. This means that the new declaratory action Aereo is seeking will not really change any facts on the ground but could give the company another favorable verdict — but not one that will determine its fate in Boston (which is in the First Circuit) or any of the other legal jurisdictions where Aereo plans to open shop.

The most likely explanation, then, is that the move is part of the increasingly pitched PR battle between Aereo and the broadcasters who, in another recent appeal, accused the upstart of creating “havoc” and “massive disruption” in the television industry. The broadcasters have also threatened to pull their signals altogether and distribute their channels, including Fox and ABC, only on pay TV.

Aereo, for its part, argues that its technology, which assigns every subscriber a personal antenna, is akin to private viewing through a DVR system.  The company’s CEO, Chet Kanojia, has accused the broadcasters of extracting exorbitant fees by forcing viewers to accept cable bundles stuffed with channels they don’t want to watch.

Aereo’s new lawsuit, therefore, gives it a way to gain the upper hand on the media message (for a short time at least) – and possibly pick up some additional legal language from a judge who has taken the company’s side in the past.

In the bigger picture, the Aereo fight is part of a great game over the future of the TV industry. Aereo, which is backed by a major investment from media mogul Barry Diller, has also been the subject of acquisition rumors by satellite provider Dish. Broadcasters fear that an alliance between the two companies could provide an end-run around the existing system that requires cable and satellite providers to pay for use of the over-the-air signals.

The final outcome could well end up at the Supreme Court given a current split between the courts in New York and a district court in California, which shut down a similar service to Aereo last year. In the meantime, it’s possible that a patchwork of decisions could result in Aereo being legal in half the country and forbidden in the other half.

In another recent development, the four major sports leagues have joined the anti-Aereo chorus by filing court papers to support the broadcasters’ request that a full panel of the Second Circuit reconsider its decision. The NFL, NBA, NHL and Major League Baseball argue that the appeals court was wrong to consider Aereo a “private” transmission like singing in the shower:

An individual who sings a copyrighted lyric in the shower engages in a private performance […] A commercial service (like Aereo) that retransmits the broadcast of a copyrighted television program to thousands of paying subscribers at the same time is not in any way comparable.

Here’s a copy of Aereo’s new lawsuit:

Aereo Complaint for Declaratory Judgment – FINAL FILED

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For the unfamiliar, Aereo is a subscription service that lets users sign up for $1 a day or $8 month to watch over-the-air TV on their mobile devices and to record shows for later viewing. The technology involves assigning two dime-sized antennas to each subscriber which beam the TV from Aereo’s offices (you can see photos of the antennas in action here).

Until now, Aereo has kept a low profile, offering its service with little fanfare in New York City. But at the Consumer Electronic Show in Las Vegas this January, it said it would roll out to 22 new markets in coming months. The decision to go live in the new areas around New York City — see the full list below — was announced by Aereo this morning and appears to be the first step in the planned expansion. Aereo is also expected to soon offer the service for more non-Apple devices; right now, users can watch Aereo on the iPhone and iPad as well as on computers via various internet browsers.

To publicize the service, Aereo said it will advertise on New York City billboards as well as major transit hubs and commuter rail services in the region.

The expansion comes as Aereo remains locked in a bitter legal battle with ABC, CBS, NBC and Fox which are suing to shut it down. The networks argue that Aereo is infringing its copyright by retransmitting its signals without permission; Aereo counters that its personal antenna system means the transmissions are private and within the law (you can read legal details here).

“Today, consumers are tethered to expensive and outdated technology that limits how, when and where they can enjoy their own television programming,” said Aereo’s CEO Chet Kanojia in the news release. “Aereo’s technology now lets us provide simplicity, ease of use and rational pricing – three things that have all but disappeared for the consumer.”

To learn more about how Aereo is disrupting TV and other cutting edge media topics, come hear Kanojia speak at paidContent Live in New York on April 17.

The list of counties that can now tune into Aereo include: New York’s Bronx, Kings, Queens, Richmond, Nassau, Suffolk, Westchester, Putnam, Rockland, Ulster, Sullivan, Orange, Dutchess; Connecticut’s Fairfield County; Pennsylvania’s Pike County; New Jersey’s Bergen, Warren, Union, Sussex, Somerset, Passaic, Ocean, Morris, Monmouth, Middlesex, Hunterdon, Hudson, and Essex. Check zip code eligibility here.

Correction: an earlier version of this article incorrectly listed Chet Kanojia’s last name as Atkins.