(Reuters) - U.S. oil major Chevron Corp (CVX.N) has evacuated executives from Venezuela after two of its workers were imprisoned over a contract dispute with state-owned oil company PDVSA, according to four sources familiar with the matter.

FILE PHOTO: The logo of Chevron is seen in their office in Caracas, Venezuela, April 18, 2018. REUTERS/Carlos Garcia Rawlins/File Photo

Chevron asked other employees to avoid the facilities of its joint venture with the OPEC nation’s oil firm, the sources said.

The arrests, in a raid by national intelligence officers, were the first at a foreign oil firm since Venezuela’s government launched a purge last fall that has resulted in detentions of more than 80 executives at PDVSA and business partners.

The Chevron workers may face charges of treason for refusing to sign a supply contract for furnace parts drawn up by PDVSA executives, Reuters reported earlier this week. The workers balked at the high costs of the parts and a lack of competitive bids.

Chevron’s move to evacuate its expatriate workforce underscores the how arduous it has become for foreign oil firms and their workers to sustain operations through Venezuela’s accelerating political and economic meltdown.

The affected staff numbers about 30 people in the coastal city of Puerto la Cruz, although it is unclear how many people Chevron has already removed from the country.

Asked about the departures, Chevron on Tuesday declined to comment on what it called “personnel matters.” Last week, the company said it was working for the release of the detained workers, Carlos Algarra and Rene Vasquez, who are represented by Chevron lawyers.

Neither PDVSA nor the government’s Information Ministry responded to requests for comment. The public prosecutor’s office, which has not publicly announced any charges against the Chevron

Read more from our friends at Reuters: