Nicole Murphy Threatened By Reps -- Stop Talking S**t On Us!

Nicole Murphy has gotten way too big for her britches now that her fiance Michael Strahan snagged the morning show with Kelly Ripa ... at least according to her former reps who say she's acting like a monster, publicly trashing and destroying their business in the process.

The ZLP Group has hired a lawyer, who fired off a nasty, threatening letter to Nicole. In the letter -- obtained by TMZ -- the lawyer claims Nicole has "started rumors, misstatements and misrepresentations" which have defamed the PR group.

ZLP's lawyer, Donald Karpel, says Murphy's smack talking has destroyed his client's relationship with QVC, several NYC fashion week designers and a TV show.

Karpel promises in the letter he will file a lawsuit against her for breach of contract (allegedly firing the firm without cause) and defamation -- based on her "poor conduct."