Now we're going to go to the shapewear war heating up right now this morning. Real housewives star of new york heather thompson and billionaire founder of shapewear brand spanx are going head to head.... See More
Now we're going to go to the shapewear war heating up right now this morning. Real housewives star of new york heather thompson and billionaire founder of shapewear brand spanx are going head to head. Abc linzie janis has the latest on this battle. Reporter: There's a shapewear showdown ramping up this morning. Hi, my name is heather thomson. Reporter: On one side heather thomson the mastermind behind yummie tunnelmie. I won't be bullied and lie down and fight it as hard as i can with my last breath I will fight this. Reporter: On the other side sarah brakely, the billionaire owner and creator of hugely popular spanx whose company thomson claims ripped off several yummie tunnelmie designs violating its patent. Oh, my god, spanx is knocking me off. Reporter: The dispute hinges on the yummie tunnelmie slimming tank, one of the most popular items in town shop in new york city. The thing that was so beautiful about this, cotton on top and girdle material in the tummy section where you need it then it has cotton on the bottom. If you wear it underneath the blouse it looks like a regular blouse. Reporter: With it worth nearly a billion dollars a year a lot is at stake. No larger growth in the lingerie industry. Reporter: Earlier this year yummie tunnelmie's lawyers wrote a cease and desist letter and overnight thomson wrote an open letter on the yummie tunnelmie website. I needed to write it down woman to woman. Reporter: Blakely isn't getting her spanx in a bunch and tells abc news spanx has not infringed on any valid patent and we will continue to make fabulous products for our loyal fans. Spanx's lawyers also filed a complaint asking a judge to rule on the disagreement in court. Do you, baby, because I'm doing me. Reporter: If they don't settle the intimate details of their businesses could soon be squeezed out for the whole world to see. For "good morning america," linzie janis, abc news, new york. Wow. Big money at stake on that.
This transcript has been automatically generated and may not be 100% accurate.