Teachers engaged in more strike activity in 2018, than in the past three decades. Additionally, the first charter school strikes occurred. However, charter school teachers may lose their ability to strike if the NLRB allows states to determine whether or not teachers can legally go on strike. In 12 states, public school teachers are allowed to strike- if the NLRB decides to “decline jurisdiction” over charter schools, it may become much more difficult for teachers to engage in collective activity.
See "Charter School Strikes Endangered by Possible NLRB Change", Robert Iafolla, Bloomberg Law, March 13, 2019