Casey Anthony -- GET YOUR ASS BACK TO FLORIDA

Casey Anthony has just been ordered back to Florida to begin probation in her check fraud case -- and she has two weeks to show up ... or else.

Casey was originally supposed to kick off her one-year probation last Friday, but the judge in the case recused himself -- and turned the matter over to Casey's murder trial judge Belvin Perry.

Perry reissued the order -- and now, Casey must report to an Orange County probation officer no later than August 26th at noon ... or she could be arrested.

Anthony's legal team had argued she already served probation time while awaiting trial -- but Perry wasn't convinced ... insisting she had to serve probation AFTER jail.