Pharisees and the Sadducees were people who questioned the integrity of Jesus and finally accused him of blasphemy and had him condemned to death by crucifixion. As an idiom it means a person who condemns an innocent person.
Example: The Police were not Pharisees when they arrested the Malayalam film star Dileep on having connived the sexual molestation of an actress.
McCarthyism in America was action of Pharisees.
Pharisees are hypocrites of the society.