For a long time, they had National League balls and American League balls, which were supposedly the same other than the markings (thought one was stamped in black and the other in light blue). Then they went to the "MLB" ball, which included the MLB logo. Pitchers went ballistic claiming that the new MLB logo stamp on the ball made it easier for hitters to see the pitch.
Now might also be the time to point out that minor league balls are made in China.