TMZ has learned at least two companies who pay for ads on Colleen's podcast have pulled their sponsorships, and it may just be the tip of the iceberg.

Here's the deal ... Colleen is under fire for a viral clip from one of her old comedy shows, which features her calling a young fan up to the stage for an embarrassing fart stunt.

In the resurfaced footage, Colleen spreads the young fan's legs as she lies on her back on stage ... and then a fart noise blares over the speakers.

A woman who says she is the girl in the video is now speaking out ... she says she was only a teenager at the time and rips Colleen for embarrassing and traumatizing her.

She's also taken heat for asking a young fan to pretend to give birth, and for other crude comments at her shows toward minors.

Some of Colleen's podcast sponsors have taken notice and taken action ... skincare company OneSkin tells us they severed ties with Colleen, saying ... "We were made aware of this previously and have decided to cease the relationship completely. This behavior is appalling and we do not condone or support it in any form."

Another advertiser, healthcare marketplace Zocdoc, says they will no longer run ads on her podcast.