Amber Portwood's Landlord -- Happy New Year, You're HOMELESS!!

Amber Portwood's landlord is tossing her out in the street -- a fact the "Teen Mom" star might care more about ... if she hadn't been cooling her ass in jail for the last 17 days.

The company that owns Amber's rented home in Anderson, Indiana filed notice with the court yesterday that it wants her out ASAP.

According to the docs, Portwood somehow violated her lease agreement -- no specifics are listed -- and the landlord delivered a "notice to vacate" on Dec. 20 ... the day AFTER Amber got hauled off to jail for alleged probation violations.

Portwood's attorney tells TMZ he didn't know about the notice, so couldn't comment. If Amber misses a Jan. 25 court date she could be evicted immediately.