Chris Harrison‘s new dating show is sparking a nasty back-and-forth between Fox Nation and Warner Bros. TV … with Fox firing back after ‘Bachelor’ producers took issue with “The Vow.”

Here’s the deal … Warner Bros. lawyers sent Fox Nation a cease-and-desist, claiming Chris’ new show is trying to ride on the coattails of “The Bachelor” … taking issue with some visuals in a new promo for “The Vow.”

In their response, obtained by TMZ, Fox Nation says … “While FOX Nation respects the intellectual property rights of others, you wrongly assume that Warner Bros. holds any rights whatsoever in a falling roses motif or in the words ‘The Bachelor’ when used colloquially to describe a single man.”

As we previously reported, Chris says in the promo … “Roses fade, true love lasts forever” – an apparent dig at his previous employers. There is also imagery of falling rose petals and rose flowers.

Fox Nation claims WB’s cease-and-desist “focuses myopically on certain stills from the trailer” instead of the actual point of including the roses … “to convey that The Vow ‘offers a different approach’ from other dating shows.”

Fox Nation says … “Your letter appears to be designed not to vindicate legitimate copyright and trademark interests, but to restrict FOX Nation and Chris Harrison from promoting a competing dating show.”

The response continues … “It is unfortunate that Warner Bros. is targeting Mr. Harrison in this malicious and vindictive manner.”

Fox Nation says the copyright claim over falling rose petals is BS … saying it’s a popular trope in romance media that “The Bachelor” actually borrowed itself.

What’s more, Fox Nation also argues that Warner Bros. doesn’t have a trademark claim over “The Vow” referring to its star as “the bachelor,” because it’s just a term to describe an unmarried man.

Fox Nation says that even if it were a tongue-in-cheek reference to “The Bachelor” … it’s wordplay and a clever allusion protected under the First Amendment.