I believe there is something in the state constitution regarding prohibition of state income tax. Additionally, remember that Texas was once an independent country, and there is something in the annexment agreement to this effect. I need confirmation on these.
Any politician who votes FOR an income tax in this state, don't even BOTHER running for re-election. Incidentally, there is a resolution in the Texas Republican Party Platform regarding being against a state income tax, which will be voted on at the state GOP convention this week.