Income inequality is taking a toll on state governments. The widening gap between the wealthiest Americans and everyone else has been matched by a slowdown in state tax revenue. Even as income for the affluent has accelerated, it has barely kept pace with inflation for most other people. That trend can mean a double-whammy for states: The wealthy often manage to shield much of their income from taxes. And they tend to spend less of it than others do, thereby limiting sales tax revenue. As the growth of tax revenue has slowed, states have faced tensions over whether to raise taxes or cut spending to balance their budgets. ''Rising income inequality is not just a social issue,'' said Gabriel Petek, the S&P credit analyst who wrote the report. ''It presents a very significant set of challenges for the policy makers.'' Stagnant pay for most people has compounded the pressure on states to preserve funding for education, highways, and social programs such as Medicaid. Income inequality isn't the only factor slowing state tax revenue. Online retailers account for a rising chunk of consumer spending. Yet they often manage to avoid sales taxes. Consumers are spending more on untaxed services, too. Before income inequality began to rise consistently, state tax revenue grew an average of 9.97 percent a year from 1950 to 1979. That average steadily fell with each subsequent decade, dipping to 3.62 percent between 2000 and 2009.