There are four types of trigger events:
Termination trigger events are most open to court interpretation.
A termination under state law is "the cessation or substantial cessation of industrial or commercial operations." The act does not give any indication as to what qualifies as a "substantial cessation" of operations. The courts have to decide what constitutes a "substantial cessation" unless it is clarified by subsequent regulations.
The other three trigger events – plant closing, mass layoff and relocation - are clearly defined under state and/or federal laws.