IRS to Sean Kingston -- You're Shorty on Your Taxes

It was back in '09 ... making money from his rhymes ... but sadly Sean Kingston didn't pay taxes on time ... this according to the IRS.

According to official documents obtained by TMZ, Kingston -- real name Kisean Anderson -- stiffed Uncle Sam to the tune of $131,379.51 for the money he made in 2009 ... the same year he released the album, "Tomorrow."

The feds warned the singer, "We have made a demand for payment” ... but since he failed to fork over the cash, the IRS obtained a lien on his property ... which means, if he doesn't pay up, the government can go after his stuff.

We’ve made repeated attempts to contact Sean’s reps for comment – but thus far, we’re getting the same treatment the IRS has gotten. A taxing effort with no results.