Gossip Girl's Leighton Meester and her mother are at odds, to say the least, and the reason the star is suing her mom is not just some petty gripe.

Leighton alleges that Constance Meester has been using considerable sums money meant for her son's medical care on plastic surgery for herself.

According to the suit, Leighton sends $7,500 a month to her mother to care for her younger brother, Lex, who suffers from severe medical issues.

Constance, in turn, uses it for plastic surgery, Botox and hair extensions.

The suit also accuses Constance of threatening Leighton with a $3 million lawsuit unless she started sending $10,000 a month instead of $7,500.

The Roommate star wants a judge to declare that there was never an oral contract in place suggesting she agreed to do so (as her mom alleges).

Constance Meester famously gave birth to her famous daughter while in federal prison for her part in a ring that smuggled drugs from Jamaica.

Earlier this year, the 54-year-old had a restraining order filed against her by Laurel Wigg, whose son attended school with Meester's son.

According to Wigg's request, Meester allegedly promised to "hunt down and kill" Wigg and her son. Leighton then fired her as her manager.