Once you become a MT resident, the income you earn by working remotely in MT for an OR employer is no longer taxable by OR, nor are OR employers required to withhold OR taxes on that income.
ALL income you earn after becoming an MT resident will be fully taxable by MT, so ideally your OR employer will withhold MT taxes for you, although they're not required to do so. If they don't withhold MT taxes, you should plan to make quarterly estimated tax payments to MT.
Once you're an MT resident, OR can still tax any income you earn from work physically carried out within OR, but they won't tax income earned from remote work done from a location outside the state. So you will need to keep track of your days worked within and without OR.
**Answers are correct to the best of my ability but do not constitute tax or legal advice.
