Dr. Daniel Barrett's been hit with a cease-and-desist letter by the couple's lawyers, who claim he's using Hailey's name, image and likeness in his video without permission to advertise his practice and "spread false, uncorroborated claims that Mrs. Bieber has undergone plastic surgery."
On top of that, Barrett's being accused of copyright infringement for his use of lyrics from Justin's song, "Sorry," in the TikTok caption.
In the vid, which was posted over the weekend, the plastic surgeon compares a 2011 photo of Hailey to a more recent one and one from 2016. He says he thinks the physical changes are impossible without some cosmetic procedures ... specifically to her nose.
Barrett also speculates Hailey's undergone genioplasty and has lip fillers.
Hailey and Justin's legal team say the TikTok includes a number of violations, including "misrepresentation, defamation, slander, false light, violation of rights of publicity, copyright infringement, trademark and service mark infringement" and more.
They're demanding Barrett take down the video and issue a public retraction in the next 24 hours ... or else the legal fury is coming.
Dr. Barrett tells TMZ ... he doesn't believe his comments in the video are disparaging, and he finds it "crazy" that the Beibers want to chase him down for something like this.
He says his video is intended to educate about plastic surgery, and he does not plan to remove it and will deal with the legal ramifications.