Bosses at Pink Taco in Century City colored the animal bright pink and emblazoned it with their logo in a bid to encourage passersby to step inside.
But, after a fan brought the stunt to Pink's attention, the animal rights activist decided to warn off all her followers on Twitter.
She wrote, "Never go to @PinkTacoLA. Pic of the painted donkey chained to wall."
And Pink's not the only star outraged by the move - reality TV star Stephanie Pratt writes, "Wow u couldn't just get a pinata?? @PinkTacoLA. Sick, evil, cruel people. I will never eat at one of ur (sic) restaurants again."
Campaigners at the People for the Ethical Treatment of Animals are said to be looking into the incident at the eatery.
The Mexican food chain was founded by Lindsay Lohan's ex-boyfriend Harry Morton.