BOGOTA, Dec 20 (Reuters) - Two unions representing workers at Colombia's principal coal railway Fenoco have reached a new salary deal with the company, Fenoco said late on Tuesday, avoiding a strike which could have stymied coal exports.

Sintraime and Sintravifer union members reached a five-year deal for a salary increase as well as transport, education and food benefits, Fenoco said in a statement. Together the two unions represent 459 of 579 workers on the railway.

Mining companies using the 226-km (140-mile) railway produce more than half of Colombia's annual output of roughly 85 million tonnes.

Fenoco transports around 44 million tonnes of coal annually from mines in northern Cesar province to Caribbean ports on behalf of U.S.-based Drummond Co, Glencore PLC's Prodeco unit, Murray Energy's Colombia Natural Resources and others.

Some users were forced to declare force majeure in 2012 because a strike prevented shipments on the line.

Colombia is the world's fifth-largest exporter of coal. Its output target for 2016 is 85.5 million tonnes.

(Reporting by Luis Jaime Acosta; Writing by Julia Symmes Cobb and Helen Murphy; Editing by Sandra Maler)