Saudi Arabia ordered its national airline not to comply with European Union emissions-trading rules in protest against the bloc’s decision to include non-EU carriers in its carbon market, two people with knowledge of the matter said.

The kingdom, OPEC’s biggest oil producer, has notified the 27-member bloc of the decision and discussions are ongoing to reach a compromise, said the people, who declined to be identified because the information isn’t public. Khalid al- Khaibary, a spokesman for the civil aviation authority in Jeddah, Saudi Arabia, declined to comment when reached by phone yesterday.

Saudi Arabia was one of the countries including the U.S., China, and India that issued a joint statement in February opposing the EU law.