Show creator Gene Roddenberry had suggested a compromise: they'd shoot two versions of the scene, one with the kiss, and one with a hug, and use whichever worked better. Everyone knew which version NBC was going to want to use, but luckily Shatner had a plan. See, a director can't see exactly what the camera is picking up -- only the camera operator can. So while they were shooting the versions of the scene that would preserve the purity of the white race, Shatner positioned himself so that the director couldn't see his face, stared right into the camera, and made a bunch of stupid faces.
Stupider than usual, which is really saying something.
The director, thinking he'd won, immediately called a wrap and sent everyone home. It wasn't until they were going over the dailies that they realized what had happened. They were forced to run the scene as originally scripted, resigning themselves to having to face an explosion of controversy that (twist!) never happened.
Truly, it was a leap forward for human rights, although whether Shatner was fighting for the progression of society or just couldn't stand to miss an opportunity to get busy on national television is anybody's guess.