BUENOS AIRES, June 15 (Reuters) - Argentina's largest oil union said on Saturday it will strike for 48 hours starting Tuesday to demand higher salaries, a move that will affect production at the giant Vaca Muerta shale formation.

The Vaca Muerta hydrocarbon formation is the world's second-largest shale gas reserve and the fourth largest for shale oil, and plays a central role in Argentina's plan to reverse a significant deficit in its energy trade balance and become a net energy exporter.

The Union of Private Oil and Gas Workers in Rio Negro, Neuquen and La Pampa - the provinces where Vaca Muerta is located- said it called the strike after talks with companies failed.

The protest will take place next Tuesday from 1100 GMT, according to a press release.

"We tried to sit down, understand, talk, reach an agreement, but they brought us the same proposals as a year and a half ago, the same thing we talked about four months ago," said the union's general secretary, Marcelo Rucci.

"We have the predisposition to dialog and to discuss. Now, what we don't have is time for them to disrespect us."

(Report by Hernán Nessi; Writing by Aida Pelaez-Fernandez; editing by Deepa Babington)