The Association of Private Sector Colleges and Universities sued the U.S. Education Department Wednesday, charging that the agency's recently enacted regulation aimed at ensuring that vocational programs prepare students for "gainful employment" is unconstitutional. The gainful employment rule, a final version of which was published last month, applies to nonprofit and for-profit colleges alike that have vocationally oriented programs, but for-profit institutions would be disproportionately affected, and a lawsuit by their chief lobbying group had been expected.