an employee is an employee and no law changes that. if you are an employee of a company in state X that does work for a company in state Y. then you have to look to several issues - do you have any physical presence in state Y? does the company that pays you have any physical presence in state Y? if both are no there would be no tax liability in state Y. if you have a physical presence in state Y, then you have to read the laws of the state to determine if you have liability - every state with an income tax has different laws. if you work from state X for your company that also has a physical location in state Y and you perform service for the Y division again state laws would determine if you have liability. in either case, most of the responsibility for reporting wages properly to the state falls on the employer.
