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KAI RYSSDAL: Northwest Airlines' flight attendants union says it's not intimidated by the mounting pressure to keep it from striking as early as Friday evening. The U.S. Justice Department and about 20 other carriers filed briefs in support of Northwest's request for an injunction to halt a walk-out. A bankruptcy judge already turned down Northwest's request for an injunction, but the airline appealed the decision.

Annie Baxter has this look at the practical and legal arguments at stake.

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ANNIE BAXTER: Northwest, the government, and other carriers are arguing that a flight attendants strike could send the country's fifth-largest airline into liquidation and disrupt the nationy's transportation system.

Aviation consultant Mike Boyd says he thinks those economic reasons are compelling enough to get a strike blocked.

MIKE BOYD: Northwest serves a lot of communities in the Dakotas and the Midwest that a lot of carriers don't serve and won't serve. So it's small communities that will get hurt real bad here.

But the flight attendants union says the alarm over a strike is exaggerated, especially since it probably won't wage a full-fledged walk-out. Instead, it would more likely use its signature form of strike called CHAOS, which involves isolated work stoppages on select flights.

Part of the problem here, though, is that this is uncharted territory in the law governing labor relations in the airline industry. Northwest says the law requires further negotiations before a strike would be legal.

But University of Chicago bankruptcy expert Douglas Baird says Northwest has already imposed a contract so the negotiating phase is over.

DOUGLAS BAIRD: And given that that's already happened, I think it makes very, very little sense to say, as a legal matter, the workers at Northwest are obliged to work under terms and conditions they never agreed to.

In the meantime, no additional talks are scheduled between the two sides. And Northwest says it's developing a "comprehensive plan" to staff flights in the event of walk-outs.

In St. Paul, Minnesota, I'm Annie Baxter for Marketplace.