Jessica Alba's The Honest Company -- Sued For Being Not So Honest

4:15 P.M. PST -- In a statement to People, Alba claimed the lawsuit was, "baseless and without merit." She says, "We strongly stand behind our products and the responsibility we have to our consumers.

Jessica Alba's billion dollar The Honest Company is under fire after one angry customer says the company isn't too honest when labeling its products as "natural" ... according to a lawsuit.

The class action suit -- filed by Jonathan Rubin targets the brand's dish soap, hand soaps, surface cleaner and diapers. Rubin claims all of the products contain synthetic preservatives and should not be considered "natural" like THC claims.

Rubin backs up his claims with studies from an environmental group who says the ingredients were considered to be potentially hazardous.

And as one final burn ... Rubin says THC's sunscreen is ineffective after multiple users posted on blogs saying they became sunburned and blistered.

He's asking for all profits generated from those products to be refunded to people who have purchased them -- a minimum of $5 million.