Eminem & Justin Bieber Smack in the Middle Of Korean Concert War

3/28/2012 5:35 PM PDT

It's the most unlikely pairing in any lawsuit ever -- Justin Bieber and Eminem -- but believe it ... because they're at the center of a new legal war over a concert in Korea ... that will never happen.

A company called Moonstone Management just filed a lawsuit in L.A. County Superior Court -- claiming it hired another company named J-Mike in 2010 to recruit either Eminem OR Bieber for a concert in Seoul, Korea ... and J-Mike never delivered.

According to the lawsuit, Moonstone paid J-Mike a down payment of $300,000 to secure one of the stars -- but J-Mike strung them along for months with nothing to show for it ... and eventually called off the deal without returning the cash.

Now, Moonstone is suing for its money back -- plus other unspecified damages.