In new legal docs ... Cardi says she's "in her final month of pregnancy and about to give birth," so she needs to push back the date of a scheduled deposition. Lawyers wanna grill her for the lawsuit a guy filed, claiming she copied his back tattoo and used it for album art.

The rapper's legal team struck a deal to move her depo date from July 25 to September 7 ... so she can get a couple months of motherhood under her belt before the grilling.

For the record, Cardi defended the album cover saying the man suing isn't a match -- and neither are his tats ...

We don't know her exact due date, but as we first reported ... it's sometime in the first week of July.