(MONEY Magazine) – A federal tax hike that took effect this year could raise your state taxes too. Under the new rule, you must reduce certain itemized deductions on your federal return by 3% of any portion of your adjusted gross income that tops $100,000. State tax experts estimate that about 30 of the 40 states with income taxes will choose to apply a similar formula to their taxes as well. Colorado, for example, has already declared that high earners will have to pay an extra $50 into state coffers for every $1,000 of disallowed federal write- offs. (Only six states -- Illinois, Indiana, Massachusetts, Michigan, New Jersey and Pennsylvania -- have officially decided not to follow suit.) As a consequence, it is even more important than ever for you to lower your adjusted gross income. Best advice: Contribute to your company's 401(k) or FSA plan. If you're self-employed, sock all the money you can into a Keogh or SEP.