The Boston Police officers formed a union, which at the time was in violation of rules the officers had sworn to. When the Police Commissioner, a man named Edwin Curtis, dropped nineteen men from the force who were leaders in the union, the union responded with a walkout of over 1100 of the force of 1500 officers on September 9, 1919. When word spread of the walkout, civil disorder broke out in the city. For two nights there was violence and rioting. Governor Coolidge had wanted to call out the State Guard when the officers left their post, but Boston Mayor Andrew Peters was worried about sympathy strikes.
Coolidge called the strikers "deserters" and "traitors" and called on the National Guard to restore order to the city. He took personal control of the police force. Union leader Samuel Gompers asked for reinstatement of the union policeman. Governor Coolidge sent a reply to Gompers saying "there is no right to strike against the public safety, by anybody, anywhere, anytime." All of the police officers who left the force to go on strike lost their jobs permanently. Coolidge said "Those who would counsel forgiveness join hands with those whose acts have threatened to destroy the government. There is no middle ground. Every attempt to prevent the formation of a new police force is a blow at the government. That way treason lies." In his autobiography, Coolidge wrote "Later I helped these men in securing other employment, but refused to allow them again to be policemen."
Although Coolidge said he did not approve of any strike, he said he understood how the officers felt as they did, when they earned less than a streetcar conductor. He received 70,000 letters and telegrams praising him for his stand, including one from Democratic President Wilson, to him, a Republican Governor, congratulating him on his reelection: "I congratulate you upon your election as a victory for law and order. When that is the issue, all Americans stand together." Coolidge said "probably no other event in my career led to my subsequent nomination as Vice-President."