H.R.6222: To amend the Internal Revenue Code of 1986 to allow a nonrefundable credit against income tax liability for gasoline and diesel fuel used in highway vehicles for nonbusiness purposes.

Working Families Gas Tax Credit Act of 2008 - Amends the Internal Revenue Code to allow a tax credit for up to $500 ($1,000 in the case of a joint return) of the cost of gasoline and diesel used in highway vehicles for a nonbusiness purpose when the increase in the price of a gallon of gasoline exceeds the annual inflation rate by not less than 300%. Phases out the amount of such credit for taxpayers with adjusted gross incomes exceeding $75,000 ($150,000 in the case of a joint return).