Credit: Dimitrios Kambouris/WireImage/Getty Images.

A New York-based law firm has followed through on a threat to file a class-action lawsuit against Kim, Khloe and Kourtney Kardashian over their endorsement of the weight-loss product QuickTrim.

According to E! Online, the firm of Bursor & Fisher has filed the five-million-dollar lawsuit in New York on behalf of four customers who allege they used Quicktrim and did not see the same results touted by the Kardashians. The customers believe the sisters' weight loss cannot be solely attributed to Quicktrim.

Both Kim and Khloe have claimed they lost 15 pounds using QuickTrim, which is manufactured by the New Jersey-based company Windmill Health Products.

The firm hinted two weeks ago to the New York Post that a lawsuit against the Kardashians, among other defendants, was forthcoming.