Kate Major's gonna pay BIG for her arrest last month -- a judge is locking her up for the next 6 months ... TMZ has learned.
Michael Lohan's estranged wife was sentenced Monday for violating probation. Her October arrest in Florida for attacking a cop triggered the violation ... according to the U.S. Attorney's Office.
Kate was already on probation for a 2015 incident in New Orleans when she allegedly got wasted on a plane and threatened the crew. Sources close to Kate tell us she asked for rehab instead of jail time but got shut down.
When she gets out of jail, Kate will still face assault, and drunk and disorderly charges for the alleged cop attack.