"When two working people decide to marry, their federal income tax is usually increased. As soon as one spouse earns at least 20 percent of a married couple's total income, the couple pays a 'marriage tax.' ... The United States is the only major industrialized nation in the free world in which the tax cost of the second [married] earner's entry into the work force is higher than that of the first. On one hand, our government's social policy is to help working women earn equal salaries to those of men, but on the other we have a tax structure that penalizes them when they do so."