Honduran trade union leader Altagracia Fuentes and two companions were murdered Thursday in the north of the Caribbean country, according to police reports.
Six gunmen wearing black and ski masks fired on the car carrying Fuentes, 60, and her companions near the city of El Progreso, 280 kilometres north the capital Tegucigalpa, dpa reported.
Fuentes was the general secretary of the Honduras' Workers Federation, the most powerful labour union in the country with some 300,000 members.
Police believe the killings were planned in advance.
In April trade unions had united in protest of the high prices for basic food in a large demonstration against the government of the liberal-conservative President Manuel Zelaya.
Fuentes had traveled to the region for an International Workers Day celebration May 1.