An oil workers' strike has halted construction of Colombia's Bicentennial Pipeline, which will be the country's longest once completed, a union spokesperson said Thursday.

A group of 40 workers hired for the initial phase of the project declared themselves on strike on Tuesday, the head of the union local in the eastern town of Hato Corozal, Alvaro Nieto, told Efe by phone.

The labor leader said the striking workers had been making progress on the base camp for the pipeline, a $4.2 billion project being spearheaded by Colombian state oil company Ecopetrol.

The initial phase of the pipeline project, awarded to Italian firm Sicim, is centered on an area of the eastern lowland province of Casanare, where most of the Andean nation's oil wealth is concentrated.

"It's a peaceful protest against abuse by the construction company, which is paying salaries below the legal limit for the oil sector," the labor leader said.

Employment prospects for the communities surrounding the project also remain unclear, according to Nieto, who said the engineering firm is expected to employ cutting-edge technology such as an automatic pipeline welding machine.

He also pointed to a lack of clarity surrounding the terms of the project's environmental permit and said the company should make the necessary investments to safeguard the environment.

"Our water resources are in danger," said Nieto, who noted that local communities support the job action because of the project's social and environmental ramifications.

The strike was declared by the Hato Corozal local of Sindispetrol, a nationwide petroleum workers' union.

The protest is the third to affect the Colombian oil industry since mid-year. The first two strikes affected the interests of Canada-based firms Pacific Rubiales and Petrominerales.

The 960-kilometer-long (600-mile-long) Bicentennial Pipeline, which will have the capacity to transport between 450,000 and 600,000 barrels of crude per day, is scheduled to be completed next year.

It will run from an Ecopetrol station at Araguaney to the Caribbean port of Coveñas.

The oil pipeline is being developed by a joint venture made up of Ecopetrol, which owns a 55 percent stake, and seven other companies, including Pacific Rubiales and Petrominerales.