IMPACT stands for the Irish Municipal Public and Civil Trade Union, and was formed in 1991 through the amalgamation of three unions, all with long traditions in the trade union movement; the Local Government and Public Services Union, the Union of Professional and Technical Civil Servants, and the Irish Municipal Employees' Trade Union.

IMPACT is Ireland's leading public sector union with members in the civil service, local government, health, education, community and voluntary organisations and semi-state companies.