Which freedom protects a labor union?
freedom of expression
freedom of religion
freedom to assemble and petition
freedom of speech

Freedom to assemble and petition.

Explanation:

According to the First Amendment Rights of the Constitution of the United States of America, the right to assemble and petition to the government gave protection to the labor unions to address their grievances. This enables them to have a certain right against being stopped or objected by any court of law. It states "'the right of the people peaceably to assemble, and to petition the Government for a redress of grievances".

it was the first amendment