In 1919, in reaction to a plan of the policemen of the Boston Police Department to register with a union, Police Commissioner Edwin U. Curtis announced that such an act would not be tolerated. In August of that year, the American Federation of Labor issued a charter to the Boston Police Union. Curtis declared the union's leaders were guilty of insubordination and would be relieved of duty, but indicated he would cancel their suspension if the union was dissolved by September 4. The mayor of Boston, Andrew Peters, convinced Curtis to delay his action for a few days, but with no results, and Curtis suspended the union leaders on September 8. The following day, about three-quarters of the policemen in Boston went on strike. Coolidge, tacitly but fully in support of Curtis' position, closely monitored the situation but initially deferred to the local authorities. He anticipated that only a resulting measure of lawlessness could sufficiently prompt the public to understand and appreciate the controlling principle – that a policeman does not strike. That night and the next, there was sporadic violence and rioting in the unruly city. Peters, concerned about sympathy strikes by the firemen and others, called up some units of the Massachusetts National Guard stationed in the Boston area pursuant to an old and obscure legal authority, and relieved Curtis of duty.