The I.R.S. has been all over Sandra Oh's ass for failing to pay taxes for a hotel job she held in 2009 -- problem is, Sandra Oh's a friggin' actress ... and SOMEONE WAS USING HER IDENTITY!!!
The "Grey's Anatomy" star rolled into an LAPD station Friday afternoon ... to report that some mystery person had been using her social security number.
Law enforcement sources tell us ... cops don't believe the scumbag was trying to pose as Sandra, but merely jacked her SS# so the person could get a job.
We're told cops are currently looking into the matter. We called Oh for comment -- hopefully the right Oh -- but so far, no word back.