The House Un-American Activities Committee (HUAC) was a federal government agency that called individuals to Congress that were suspected of being communists or had connections to the Soviet Union. This witch hunt for communists often trampled on peoples civil liberties, including their 5th amendment rights.
In the political cartoon you are referencing, the artist is implying that the federal agency will do anything in order to find communists. If this means accusing/hurting innocent people, they will do it. In the cartoon this is evident, as one of the gentleman says "It's okay....we're hunting communists."
