[norwaypinesavage]

CA has been doing this for at least decades. I married my wife in the ‘70s. She had worked in CA for a bit, before she left the state mid-year, and moved to Michigan where we were married. She earned too little in CA to owe taxes and expected a refund of the amount withheld there.

However, we filed a joint federal return. The CA return required that we also file a joint CA return. In filling that out, CA required that we include ALL of my Michigan income to the bit that she earned in CA and pay CA taxes on it. We were allowed to deduct the amount paid to MI, which was much lower than the CA amount.

In other words, I was required to pay the higher part of California taxes on all of the money I earned only in Michigan.

[Myrddin]

My employer has a presence in every state and many countries. When we do work, we have a default "zip code" for the standard office location. When we leave our default location, we must track time work and record the zip code. The payroll processor tracks income earned in each zip code and aggregates state income tax owed on the amount earned in that state.

I live in Idaho and my "default" is my home office. Some years I have to visit the project office in San Diego and provide support to staff in Omaha, NE. The consequence is a W2 for Idaho, CA and Nebraska. I have to file federal tax and state for ID/CA/NE. The cost of purchasing the state specific TurboTax edition for each state and the filing fees often exceeds the refund of the taxes collected. It's a nuisance in time spend and money spent to keep the state tax entities at bay. Each state agreed to the arrangement with my employer. Sometimes they "win". Usually they don't.