The teachers unions have no interest in the teachers. The unions want the Health and Welfare funds. To be more specific the management of those funds. In Wisconsin the teachers health insurance sponsored by the union had to lower their premiums once competition was allowed. Before the union had a sole lock on that contract. Unions have notoriously high costs in the administration of their retirement funds.
Most cities would find that teachers themselves would work with them on the issues of wages, retirement, and insurance in such a way as to save the districts money and teachers making more money at the same time.