HOUSTON (Reuters) -Venezuela's state oil company PDVSA has canceled several authorizations it had granted to its joint venture partner, Chevron ( CVX ), to load and export Venezuelan oil this month, three sources with knowledge of the decision said on Thursday.

Two of the cancellations involve tankers that had already loaded, so the oil would have to be returned to ports, while a third had not loaded, one of the sources said.

PDVSA and Chevron ( CVX ) did not immediately reply to requests for comment. It was not immediately clear if the cargoes would be rescheduled as Washington had given Chevron ( CVX ) until late May to wind down exports from the country.