The Biggest Loser contestant Tara Costa is being sued by a fitness company, who claims she violated their business agreement by gaining "a lot of weight."

The 23-year-old, who appeared on NBC's The Biggest Loser: Couples 2 and lost 155 pounds, is being sued by FC Online Marketing, Inc. for the excess weight she gained after the show.

"She came on at a certain weight. We had a fitness clause. She was in material breach after she gained, in my opinion, about 45 pounds. She was supposed to visit 15 of our franchise locations, but we weren't able to send her anywhere because she gained a lot of weight," FC Online Marketing chief executive Michael Parrella told Newsday.

FC Online Marketing, Inc., which owns the website I Love Kickboxing, claimed that the alleged weight gain ran contrary to a passage in the agreement that Costa "agrees to maintain her current level of fitness and conditioning" during the length of the agreement.

The company no longer saw Costa fit to represent the brand in 2011 after she made a guest appearance on The Biggest Loser and weighed in at 161 pounds -- a full 22 pounds heavier than in 2009.

Despite charges, Costa has continued to motivate her followers through her personal Twitter account. Recent pictures and workout statuses suggest Costa is still working toward a healthy lifestyle.

Watch The Biggest Loser star at the beginning of her weight loss journey.

Tags: Biggest Loser the biggest loser