They say the perfect worn-in denim is a bit dirty, but Levi's was probably thinking more about underhanded tactics than hygiene when it hit fellow jeans brand Evisu with a lawsuit.

The iconic denim company filed a trademark infringement suit in the U.S. District Court in San Francisco two weeks after Evisu announced plans to launch a Private Stock collection, reports WWD.

But rather than come up with, say, a few new styles, Evisu was intent on paying tribute to the Levi's of old -- namely, the 1944 501 jeans, 1890 Nevada design, and 1917 Campbell style.

At the time of the collection's announcement, Evisu's CEO Scott Morrison claimed the brand was "merely taking inspiration from our past and paying homage to one of the oldest, or historically relevant, jeans in existence, which in this case happens to have been an amazing pair of Levi's," reports the fashion news site.

"We're not remaking a Levi's jean, nor are we claiming that this is a Levi's jean," Morrison added.

Levi's isn't buying Morrison's excuse.

Apparently, this legal clash of the denim titans is part deux of a long-standing affair. Levi's previously sued Evisu in 1999 over pocket designs that were allegedly too similar to Levi's own trademark and also over some earlier styles that used the name "Evis."

According to the defendant's bio on Evisu's Web site, founder Hidehiko Yamane originally called his jeans Evis after the Buddhist god of prosperity. Even so, Levi's came home with an injunction against Evisu in that suit. Now, the San Francisco-based company is alleging that Evisu has breached the 1999 injunction.

Levi's lawyers point out that images of Private Stock jeans were posted on the defendant's Web site (they weren't in the online shopping section when StyleList checked today, but unidentified pairs could have been featured in the artsy 2010 preview photos), and that the press release announcing the collection contained the name Evis, reports WWD.

A quirk in this whole court ordeal is that the injunction's terms don't apply to Evisu in Japan, where the brand currently offers jeans with red tabs on the pocket.

Speaking of dirty denim, the cutthroat jeans industry has inspired a documentary.