If you mean software engineers when saying "tech workers" because unions make it harder to fire people. There's not much that makes a software engineer's job harder than a bad engineer who isn't getting fired and is destroying the quality of the product and the code and creating work for everyone else to fix, all the time.

Unions also result in gaining seniority by time spent in a job instead of competency, and that's also a miserable experience, when someone incompetent is dictating the engineering work. In software engineering you want people who are technically proficient and capable of mentoring to assume leadership positions and positions of increased responsibility, not people who've been there the longest.