I have a similar problem. My employer has "bricks and mortar" in every state and 30 countries. When I travel to another company location, I'm compelled to record the zip code on my time card. The consequence is that I have to file income tax in CA and sometimes NE in addition to my state of residence, ID. CA taxes me, but I have no voice as a voter since I'm an ID resident. Taxation without representation. Frankly, I pay more CA state income tax than many CA state residents.
This year I'm trying to avoid any more visits to San Diego than absolutely required. Instead of the original "one week per month", I've restrained it to one visit total in 2017 as of the current time. Thus far, no calls to Omaha. It only takes ONE visit to either spot to force a W2 and extra state filing.
City attorneys said the pesky 1st Amendment wouldn't allow it.