Baseball Card WAR -- Topps Sues Over Mickey Mantle Card

One of the GREATEST YANKEES OF ALL-TIME has been thrust into the middle of a showdown between two HUGE baseball card companies ... TMZ has learned.

The Topps Company has filed a lawsuit in NY against Leaf Trading Cards -- claiming Leaf is using ICONIC Topps baseball cards -- including the 1952 Topps Mickey Mantle rookie card -- to promote a new Leaf product.

It's sorta weird -- Leaf has a new line of cards called "2011 Best of Baseball" ... and in every pack, collectors will get 1 new, original Leaf card and 1 bonus card which, depending on your luck, could be a pre-1970 card featuring a Hall-of-Famer.

According to the lawsuit, Leaf put together a promotional ad (above) featuring some of the bonus cards -- which include the Mantle card, a 1980 Topps Rickey Henderson, a 1972 Topps Carlton Fisk card and more.

Topps claims it had warned Leaf about a similar incident in 2010 ... but now, Topps' patience has run out ... and it wants Leaf to pay up. Topps is suing for unspecified damages AND it wants a judge to force Leaf to STOP using Topps cards to promote Leaf products.