Nicki Minaj's lawyers say they're tired of repping the rapper in one of her lawsuits … and they are asking the judge to let them bow out of the case ... TMZ has learned.

According to new legal docs obtained by TMZ, the law firm Kurzman Eisenberg Corbin & Lever wants permission to withdraw from representing Nicki and her Pink Friday Productions company in the lawsuit filed against them by 24/7 Productions.

The suit claims Nicki and Pink Friday Productions failed to reimburse over $200K in expenses 24/7 says they incurred in connection with her "Pink Friday 2" album.

The lawyers hired to defend Nicki in the case now want out due to "irreconcilable differences" concerning the "conduct of the representation."

The firm said there's been a breakdown in communication with Nicki … and they don't believe they can keep working for her. They say they've tried to let her know about their decision but are struggling to serve her.

Per the docs, a man hired to serve Nicki said he went to the building where she lives in a $10 million penthouse ... but claims the concierge said Nicki was not home, but her husband was … and also told him the couple had a "tendency of not answering their phones."