A strike by union members during a valid contract period is classified as what?

A strike by union members during a valid contract period is classified as illegal primarily because it breaches the terms of the existing collective bargaining agreement. When a union and an employer agree on a contract, it typically includes specific obligations and commitments from both sides, which are legally binding for the duration of the contract. Engaging in a strike during this period undermines those obligations and is seen as a violation of the contract terms.

Unions are generally expected to honor existing contracts until they have either expired or been renegotiated. Striking while a valid contract is in place can disrupt operations and lead to legal repercussions for the union and its members, which is why it is categorized as illegal. This classification emphasizes the principle that parties in a contract must adhere to its terms until they are legally modified or terminated.