Sibling spat!

Jessica Simpson's birthday trip to St. Barths has made the rumored feud between her and pregnant sister Ashlee even worse, Life & Style reports.

Evan Ross' expectant wifey is furious at Jess for taking their mom Tina on vacay with her so close to her late July due date.

"Ashlee could give birth any day now. She’s very upset that Jessica would plan this big trip with their mom right now, during her time of need," a source dished to the mag.

She also didn't care for the fashion mogul's opinion on how she decorated her unborn baby girl's nursery! "She wanted her opinion, but she didn’t think Jessica would tear all her choices apart. Jessica criticized everything from the furniture to the baby clothes. Ashlee had decorated the nursery herself and she was very proud, and Jessica really hurt her feelings," the source added.

Ash decided to hit back by pointing out the twice married singer's out of control drinking and bad parenting! Ouch! "They both said some things they’ll regret. Their mom wishes they’d make up, but it’s probably best they spent some time apart,” the insider revealed.

She better be careful not to bite the hand that pays her!