Isn't this ILLEGAL too?

TEACHERS TOLD NOT TO WEAR OBAMA BUTTONS - New York Post:

"The teachers union has been handing out thousands of Barack Obama campaign buttons to its members, sparking a clampdown by education brass."

I always thought it was ILLEGAL for unions to show support for one party over the other, or to try to influence the voting habits of their members? In fact I'm sure it is a FEDERAL offense ... not one that can be linked directly to Obama or his campaign ...

but one that could force the dismemberment of the union itself!

then where will the teachers be??