This paper examines how low-income single parents alter their regular and informal labor supply in response to the earned income tax credit (EITC). Variation in state EITCs from 1997-2005 identifies changes in informal and regular labor supply of unmarried low-income parents in response to tax credits. The informal-sector participation of single fathers declines by 7.3 percentage points, conditional on working in the regular sector, if a state EITC increases by 10 percent of the federal credit. Regular-sector hours worked per week increase by 4.5 hours and informal sector hours per week fall by 2.2 hours with no significant effect on total hours.