Employment Law Questions? Ask an Employment Lawyer.
There are no major differences in the employer-employee relationship structure. Both states follow the "employment at will" doctrine with regard to non-contract employees.
The biggest difference is probably in the area of "right to work" law. Arizona is a right to work State, while Washington is not. All this means is that an employee can't be forced to join a union and pay dues in Arizona, while they can in Washington.
The other major difference is the minimum wage. Arizona is $7.65, while Washington's is quite a bit higher at $9.04 per hour.