China banned pigtails in 1911.

The pigtail was meant as a symbol of submission to the Qing Dynasty, and the Han Chinese were obligated to wear the pigtail. When the Qing Dynasty fell in 1911, this hairstyle was banned. However, China wasn’t the first place to ban pigtails. In 1873, a San Francisco ordinance banned pigtails for prisoners. This was during a wave of Chinese immigrants coming to San Francisco. A large number of impoverished Chinese immigrants were living in overcrowded boarding houses, in violation of the Sanitary Ordinance. Rather than follow the ordinance, the immigrants opted instead to go to prison for the free room and board. The prisons were getting overcrowded, so the pigtail law was enacted to try to discourage the Chinese immigrants from going to prison.
(source)