Basically that's it. He was a food market owner and he announced he would not carry products made by advertisers who supported communists on TV and radio. The advertisers (who owned the shows in those days) demanded that the broadcast networks fire the communists or fired them themselves. This became the "Hollywood blacklist". Someone wrote a book at the time "Red Channels" making further accusations.
My question is _how_ one person could intimidate big national consumer product companies and networks into fear. So even if this guy goes through with this threat, he's only one grocer in a small city. There are other grocers in that town and of course other cities. I don't understand how this one single guy had so much influence.
I mean, today lots of special interest groups pressure advertisers to do this or not do that on the threat of a consumer boycott. Even though these groups are pretty well organized their threats are ignored.
One time, out of fear, The WB TV network pulled off a show. The actors who worked for The WB were outraged and were ready to boycott. Actually, under the specific circumstances at that particular time, postponing the air date was not a bad idea.