popular designation of the Political Activity Act, passed by the U.S. Congress in 1939 and amended in 1940, forbidding federal employees to engage in certain types of political activity and placing ceilings on campaign expenditures. The act is named for its author, Senator Carl Atwood Hatch (1889–1963) of New Mexico. An earlier Hatch Act (1887), named for Representative William Henry Hatch (1833–96) of Missouri, concerned the study of scientific agriculture.

Among its provisions, the Hatch Act prohibited such practices as threatening, intimidating, or coercing voters in national elections; made it illegal for administrators in U.S. civil service to interfere with the nomination and election of candidates to federal office; proscribed the practices of promising and withholding certain kinds of employment and unemployment relief as a reward or punishment for political activity; and prohibited the solicitation of political contributions from relief recipients.

The Hatch Act was amended in 1940 to put a $5000 ceiling on annual individual contributions to campaigns for any one candidate for election to federal office and to limit the contributions received and expended by political committees to $3 million a year. The purchase of goods or advertising, the proceeds of which would benefit candidates for election to federal office, was prohibited. All provisions of the act relating to federal employees were extended to state employees engaged in any function financed by federal funds. Later statutes, especially those of the 1970s, dealt with the use and limitation of campaign contributions. The Hatch Act Reform Amendments of 1993 liberalized restrictions on partisan political activities by off-duty federal employees.