The suit alleges that students in California public schools are harmed because of the ineffectiveness of poorly-performing teachers, whom school districts are unable to terminate because of tenure. A combination of State statutes and processes make it next to impossible to get rid of tenured bad teachers.
The vast majority of teachers are hard-working individuals who care deeply for the students they instruct. Roughly 60% of teachers in CA have tenure. The target of the suit are those tenured teachers that are ineffective in the classroom. Although it's theoretically possible to terminate these employees, in practical terms only about 10 tenured teachers out of 290,000 in the state are actually fired each year.
The suit is against the State of California, asking for a change in law and process. The suit is NOT targeting teachers or teachers' unions, at least not directly.
School districts support the lawsuit. The superintendent of the LA schools, John Deasy, supports it. However, the CA teachers' unions are against the lawsuit. You have to ask yourself: Why wouldn't the unions have the same desire as parents and students in removing bad teachers? Bad teachers aren't just bad for students, they're bad for everybody.
Try turning the question around, and ask: How do the unions benefit by having bad teachers? The answer is simple. Unions benefit from large numbers of dues-paying members. The more members, the more dues, and the more the unions can spread those dues to further their own interests. A bad teacher's lifeline is the union. The union makes it possible for the bad teacher to continue getting a paycheck. A bad teacher is the union's strongest supporter.