Kylie and Kendall Jenner's Companies Sued Over Lacy Underwear

Kylie Jenner's undies might be hot sellers, but they're also a ripoff ... at least according to a company claiming she and her sister, Kendall, stole its lace design for their lingerie line.

The Jenner sisters just got slapped with a lawsuit filed by Klauber Bros., Inc. -- which designs 2-dimensional artwork for purpose of lace production. Yeah, apparently that's a whole industry. Anyway, Klauber says it made a couple of very specific lace designs. So specific, it even has copyrights on 'em.

Now, we don't often hear anyone complain about Kylie or Kendall in thongs ... but Klauber's got beef with a few of their underthings. According to docs, obtained by TMZ, Kylie Thong Panties uses one of Klauber's lace patterns on its waistband. Ditto for a Kendall + Kylie lingerie item we'll call a slip. We're no experts.

In the suit, Klauber says the sisters' companies are cashing in on its copyrighted designs by hawking their sexy wares in Nordstrom and on Kylie Shop, her online store -- and without permission.

Translation: We need to get paid for those panties!

Klauber is suing to get ALL the profits KJ and KJ have netted off any designs using its lace. As you can imagine -- that would be a LOT o' dough.

We've reached out to reps for both Jenners ... the billionaire mogul and the model.