Definition of 'Unofficial Strike'
A work stoppage by union members that is not endorsed by the union and that does not follow the legal requirements for striking. Workers engaging in unofficial strikes have little legal recourse if they are fired and do not receive strike pay.
Also called a "wildcat strike" or "unofficial industrial action."
Investopedia explains 'Unofficial Strike'
In the United States, this type of strike is illegal under the 1935 National Labor Relations Act. In the U.K., unions can be held vicariously liable for the actions of unofficial strikers unless they formally repudiate the strike and order the strikers to return to work.
Well-known unofficial strikes include the 2007 unofficial Royal Mail postal strike in the U.K. over working hours and the 2009 U.K. Lindsey Oil Refinery strikes over a construction contract.