If a state seceded from the United States, would its residents still owe US federal income tax under US law?

Question

Assume Texas' threat to form a union of states materializes and those states break away and begin levying their own taxes. The USA continues to claim that territory but has no de facto control.

Are individuals in the rebellious states liable for federal taxes? If a state breaks away, can the IRS still try to collect taxes in that state, or is there some tax rule stating that things change?

If it was 1861 (or whatever), the Confederate citizens would have an enormous IRS bill in 1865, but that didn't happen because income tax didnt exist.

Answer 1

Yes, they will continue to owe taxes

... and fines and interest on those unpaid taxes.

In the wake of the Civil War, the legal issue as to if any part of the USA could break away without the consent of the Federal government was settled decisively: no.

Therefore, any such breakaway territory is still part of the USA, and any taxes owed remain owing until they are paid. You don’t discharge a debt by paying money to someone who is not the debtor.

Answer 2

is there some tax rule stating that things change?

There isn't. US citizens are required to report their worldwide income to the IRS, and to figure their tax on the basis of their worldwide income, no matter where they live.

If the states' secession is recognized by the US government then there would be a negotiated agreement with terms governing all sorts of things that need to be taken care of in connection with that secession, not unlike the negotiations currently under way between the United Kingdom and the European Union. (There would probably also have to be an amendment to the US constitution.) In that case, the answer to this question would depend on the outcome of those negotiations. Presumably the negotiations would include some mechanism for the residents of the states leaving the union to lose their US citizenship, along with changes to the Internal Revenue Code.

If the US does not recognize the secession then there won't be a secession. The states would not be able to deploy sufficient military force to assert control over their territory. The US citizens in those states would therefore remain US citizens, liable to the IRS.