IRS to Lionel Richie: Hello ... It's $1.1 Million We're Looking For

For most people ... a $1.1 million debt to the IRS is a REALLY BIG DEAL ... but when you're Lionel Richie and worth an estimated $200 mil ... it's probably just a nuisance.

According to documents obtained by TMZ ... Richie owes the federal government $1,130,609.11 in unpaid income tax for 2010.

The singer has been slapped with a lien ... which means Uncle Sam can start going after his stuff if he doesn't fork over the dough ASAP.