Ministers from the Organization of the Petroleum Exporting Countries and its allies, a group known as OPEC+ that includes top producers Saudi Arabia and Russia, are scheduled to gather on Saturday and Sunday for a regular biannual meeting. The group pumps more than 40% of the world's oil supply.

The Reuters text journalists that cover meetings and are registered with OPEC as members of the press have not received an invite to cover the event.

OPEC has also not offered accreditation to Bloomberg to cover the meeting, a Bloomberg News spokesperson said on Wednesday.

Two reporters from the Wall Street Journal who regularly cover OPEC have also not received invites, people familiar with the matter said. The Journal did not respond immediately to requests for comment.

Reuters has not received a response to a request for comment from OPEC on why it has not sent invitations to Reuters reporters to cover the meeting.

"We are disappointed that Reuters has not been invited," said a Reuters spokesperson.

"We have reached out to OPEC for clarity on the matter. We believe that a free press serves readers, markets and the public interest."

Without an invitation, journalists will not receive accreditation to enter the OPEC Secretariat where the ministers meet, or attend the press conference at the end of the event, an OPEC source said.

The Financial Times reported in a story on Wednesday that it had received an invite.

Reporters at some other media outlets including CNBC, and pricing agencies Argus and Platts said they have received invitations to cover the meetings. Argus, Platts and CNBC did not respond immediately to requests for comment.

"Please note that this invitation is exclusive to the recipient," said an invitation from OPEC's Public Relations Department seen by Reuters and sent to a journalist at another media outlet. Reuters saw invites to two outlets.