A new lawsuit seeks to block the public from voting on a proposed constitutional amendment that would limit tenure protections for public school teachers. The lawsuit filed today contends that the proposed ballot initiative is unconstitutional because it effectively would change two parts of the constitution — one dealing with education, the other with collective bargaining. Two teachers from the Francis Howell School District are the plaintiffs in the lawsuit, including one who serves as president of the local chapter of the National Education Association. Supporters of the initiative submitted petition signatures last month to get the measure on the November ballot. The proposal would limit teachers to three-year contracts and require their evaluations to be based on student performance.