According to legal docs, obtained by TMZ, Benjamin Bunn claims Christmas told him he was the father, and he took care of the reality TV star during her pregnancy ... but Benjamin claims Christmas has been keeping him from the child.

Benjamin claims Christmas has refused to voluntarily submit a genetic marker test, so he's seeking a paternity test to settle the matter once and for all.

Christmas gave birth last month in North Carolina, and Benjamin claims they were planning to raise the kid in Florida. But, Benjamin says Christmas abandoned their plan after she had an altercation with his side chick in Tampa, returning to N.C. with the kid, and they've gone MIA.

As we reported ... Christmas turned herself into Florida authorities this week and was booked for felony criminal mischief, after allegedly confronting Benjamin's side chick outside a Tampa gym and ramming into the woman's car.