Use the term red scare when you're talking about a time in history when a group or government promoted a fear of communism that spread widely through the population.
The most well-known red scare was also known as "McCarthyism," after the US senator who stirred up anti-communist ideas in the 1940's. The result of the red scare was that people became afraid of being associated with communists or labeled communists themselves. Those who were considered communist sympathizers often found themselves blacklisted, or placed on a list that blocked them from getting jobs. The term red scare comes from the historic connection of the color red with communism.