In the light of ever increasing legal restraints on industrial action both here in the UK and in the USA (particularly in the 'public services') and the collusion of unions with the professional politicians to control disputes this recent attempt by teachers in Detroit to circumvent those restraints with an unofficial coordinated 'sick-out' is worthy of note;
See here: www.leftcom.org/en/articles/2016-02-14/detroit-teachers-sickout and some more details on this trotskyist site here: www.wsws.org/en/articles/2016/02/11/teac-f11.html
Other NA comrades might also be able to comment on this.