The proposed class action lawsuit takes aim at the sisters' endorsement deal with the weight loss company. It was filed on Thursday in federal court in New York on behalf of four plaintiffs who used the product.

The plaintiffs, who live in New York, California and Florida, stated in their lawsuit that the claims made by QuickTrim and by the Kardashians marketing it were "false, misleading, and unsubstantiated."

They added there was "no competent and reliable scientific evidence supporting any of these claims."

The main ingredient in the pills is a large dose of caffeine, mixed with herbal ingredients never clinically proven as effective, the lawsuit stated.

The lawsuit, which was filed by the law firm of Bursor & Fisher, must be certified by a judge as a class action complaint before it can cover a wider field of consumers than the four plaintiffs. The suit seeks over $5 million in damages.

A representative for the Kardashians and officials from QuickTrim could not be reached for comment about the lawsuit.

This is not the first time the stars of "Keeping Up With the Kardashians" on cable network E! have been at the center of litigation over their marketing endorsements.

Those deals account for a substantial chunk of the family's net worth, last estimated at $65 million in 2010 by industry trade magazine The Hollywood Reporter.

Kim Kardashian, 31, is one of the highest paid reality stars on U.S. television, with her 2010 earnings estimated at $6 million from her TV show, clothing line and numerous fitness, beauty and other product endorsements.

Her sisters, Khloe and Kourtney, have also gained fame alongside Kim, who first caught public attention when she appeared in a 2007 sex tape.

Early last year, all three Kardashian sisters and their mother Kris Jenner successfully fended off a $75 million lawsuit from a credit card company after they walked away from a debit card endorsement, "Kardashian Kard," amid complaints about high consumer fees.

(Reporting By Piya Sinha-Roy: Editing by Alex Dobuzinskis and Tim Gaynor)

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