There were not a lot of options.
--You could fight it but could except to still lose your job.
--You could admit to it and be considered an enemy of the state.
Ultimately if someone accused you of being a communist in during the Red Scare you would have to undergo investigation. You should expect that you would be judged by family, friends, and employers. Many were "blacklisted" or even fired from jobs due to the accusation.