I'm retiring to a state with no income tax. Can my former state tax my retirement benefits?
The short answer is "no."
In the past, several states enacted "source tax" laws that attempted to tax retirement benefits if they were earned in that state, regardless of where a taxpayer resided when the benefits were ultimately paid. For example, if you earned a $50,000 annual pension while working in California, and then retired to Florida, California would attempt to tax those benefits, even though you were no longer a California resident.
But, in 1996, a federal law was enacted (P.L. 104-95) that prohibited states from taxing certain retirement benefits paid to nonresidents. As a result, if your retirement benefits are covered by the law (most are, see below), only the state in which you reside can tax those benefits.
...
The law applies to all qualified plans. This includes 401(k)s, profit-sharing plans and defined benefit plans, IRAs, SEP-IRAs, Internal Revenue Section 403(a) annuities, Section 403(b) plans, Section 457(b) plans and governmental plans.