*Now that her fiancé, Michael Strahan, has been tagged to co-host “Live” with Kelly Ripa, her former reps say she become a bullying monster.

She’s been publicly trashing and destroying their business in the process and they want it stop.

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.”

So far, no comment from Murphy.