This FAQ is part of the Ask Sam Series, sponsored by Samuel F. Wright, Captain, JAGC, USN (Ret.) For voters who like to get down to the nitty gritty...
Short Answer First: If you are indefinitely overseas, you should vote only for Federal offices - President/Vice President, U.S. Senate and U.S. House of Representatives - (not state or local level offices.
A friend of mine told me that if I vote by absentee ballot in State A in the 2008 Presidential election, State A will then be able to impose on me its state income tax, not just for 2008, but for the whole time since I left State A to move to Europe. How does this work? Does my voting by absentee ballot have any effect on my liability for state income tax?
UOCAVA is a floor and not a ceiling on your right to vote while overseas. If State A, by state law, chooses to allow someone in your situation (gone from the state for several years and with no specific intent to return at a date certain) to vote a full ballot (including state and local offices), that would not violate UOCAVA.
UOCAVA provides as follows on the question of the effect of voting on tax liability: The exercise of any right under this title shall not affect, for purposes of any Federal, State or local tax, the residence or domicile of a person exercising such right. 42 U.S.C. 1973ff-5. Under Article VI, Clause 2 of the United States Constitution (commonly called the Supremacy Clause), a Federal statute (like UOCAVA) supersedes and overrides a conflicting state statute or state constitution.
If you vote FOR FEDERAL OFFICES under UOCAVA, it is unlawful for State A to use the fact of voting to establish your liability for the state income tax. On the other hand, if you were to vote a FULL ballot (including state and local offices), it would be arguably permissible for State A to use the fact of voting as evidence of your liability for the state income tax.
I suggest that when you apply for an absentee ballot, you should make clear that you are only eligible to vote and only wish to vote for Federal offices, and request that the election official send you a ballot that is limited to Federal offices. If the official nonetheless sends you a full ballot, you should only mark it for Federal offices. Then, you should send the official a separate letter, in a separate envelope, and point out that you had requested a ballot that was limited to Federal offices and that you only marked your ballot for Federal offices. (Do not include this letter in the same envelope with your marked absentee ballot, because notes accompanying absentee ballots are generally neither read nor preserved.)Keep a copy of the absentee ballot request and the letter, just in case.