Then why doesn’t he want them to go for police and fire unions as well?
One thing at a time. Get the SEIU and teachers first, then work on refining the contracts of the first responders.
It could possibly precipitate a national crisis if the first responders decided to walk off the job in support for the SEIU.
Besides, the first responders are a unique group of people, who may need and deserve public support in exchange for the job risks involved.