'Project Runway' Winner Christian Siriano's Company Sued Over Panties and PJs

Christian Siriano allegedly tried pulling a classic retail move on a company that wanted to use his name on its gear ... by taking back the deal.

The "Project Runway" winner's company, Christian Siriano Holdings, was just sued by M&A Imports for allegedly breaking a contract he signed in 2015. The deal gave the company permission to slap Christian's name all over its women's line -- panties, bras, PJs and the like.

M&A -- which owns the famous Just Love brand -- claims its agreement with Siriano gave them exclusive rights to plaster 'Christian Siriano New York' on its products for a minimum of 3 years, but he pulled out last month without explanation.

In the docs obtained by TMZ, M&A says his abrupt U-turn cost the company a fortune ... to the tune of more than $10,000,000. They're asking a judge for at least that much ... plus interest.

We've reached out to Siriano's camp for comment ... so far no word back.