Tenure does not provide much protection in biomedical research—only funding. In fact at top tier institutions tenure is almost meaningless often with <50% salary guaranteed even with a teaching load.

I think the abuses of seniority are much less than in the past—both wrt extraneous labor (hey, help me paint my house) to sexual pressures.

Re unionization—-its complex and a function of teaching load as a TA versus, class work as a student, versus your own research with mentors.