A more thorough explanation:

Definition: An escape period is a period of time specified in some union contracts during which workers have the option to withdraw from the union before the start of the next term covered by the contract.

For example, if a union contract is for three years, with an escape period of one month before the end of each year, workers can choose to leave the union during that one-month period without penalty or repercussions.

The purpose of an escape period is to give workers the opportunity to reassess their membership in the union and decide whether or not they want to continue their membership for the next term.