In new court docs, obtained by TMZ, BRC claims his estranged wife Firerose put 37 unauthorized charges onto his business American Express card between May 23 and June 7 ... totaling a whopping $96,986.05.

Cyrus claims Firerose overcharged the account without his knowledge, adding he never gave her access to the cards or his accounts in general ... pointing to the fact they did not file a joint tax return as alleged proof.

InTouch Weekly first reported ... Billy Ray is asking a judge to approve an emergency motion to prevent Firerose from accessing his financial accounts and to reimburse him for the unauthorized charges ... but like we said, Firerose has offered up an explanation in her own court docs, and she calls BS.

From her POV, Firerose claims there's no emergency in this situation, and insists Billy's mistaken about what she had access to and when -- claiming she's been allowed to use his credit cards since she moved in with him in 2022 -- adding she was never confined to a limit.

In fact, Firerose claims she's only maintained her already-established lifestyle ... and, she should be allowed to continue using his money for her personal and household expenses, as well as attorneys fees, while they're married.

Speaking of which ... the law firm representing Firerose is saying it returned about $45,000 to Billy at this point -- explaining it meant to charge Firerose just $5,000 in that transaction ... as opposed to $50,000 ... which is what Billy says showed up on his credit card statement.

Of course, this drama comes on the heels of Billy Ray filing to annul his marriage to Firerose, claiming the marriage was obtained via "fraud." Important to note, this filing over credit card charges is separate from the initial divorce and annulment filing.

So, it's unclear if Billy is pinning the annulment filing on this ... or something else entirely.

Either way ... things are getting ugly -- which is a shame considering these two were madly in love. Billy and Firerose got engaged in August 2022 -- just months after longtime spouse Tish Cyrus filed for divorce from him. Billy and Firerose got hitched in October 2023.