A wildcat strike is a strike action which is undertaken while a union contract is still in effect, or while a union is negotiating for benefits. Since a wildcat strike is not authorized by a union, it is technically an illegal action. In most countries, employees who participate in a wildcat strike can be dismissed without legal repercussions for the company. Because wildcat strikes are not legally protected, most workers try to avoid them.

In labor terms, a strike is a stoppage or slowdown or work which is designed to force a company into making concessions. There are a number of different styles of strike, ranging from strikes in which workers all simultaneously call in sick in a “sick-out” to a strike where workers picket their company in order to draw attention to the cause. In many countries, better labor laws and union protections have made strikes much less common. Striking workers also enjoy certain legal protections, such as the right to return to work.

Many modern workers are organized in a union, which bargains on behalf of the protected workers. A union may also call for a strike or another sort of protest action, if it deems the action necessary. In this case, the strike is legally permitted, because it is authorized by the union. Typically, a union will notify a company that a strike is imminent, allowing the company to decide whether to concede to the union's requests or to deal with the strike.

When a wildcat strike is organized, workers strike without the benefit of union protection. There are a number of reasons to organize a wildcat strike. In some cases, workers may feel that the union is not doing enough to protect them, so they strike on their own to force their company to pay attention to the issue. A wildcat strike may also occur when a serious safety issue is not addressed, or when workers want to protest a dismissal which they believe to be unfair.

Unlike a regular strike, a wildcat strike appears with no notice. The striking workers may picket the company to highlight the cause and force temporary workers out, or they may simply choose not to come to work. In some cases, a wildcat strike lasts only a day, and is held more to make a point than to decide a major issue. In other instances, a wildcat strike lasts until the perceived problem has been addressed or corrected.