NEW YORK (Reuters) -The U.S. Federal Trade Commission allowed Chevron's ( CVX ) $53 billion purchase of Hess Corp ( HES ) on Monday, in an order that barred Hess CEO John Hess from Chevron's ( CVX ) board.

The FTC's order leaves Exxon Mobil's ( XOM ) challenge to the deal, which is expected to stretch deep into next year, as its final hurdle.

The proposed merger included a Chevron ( CVX ) board seat for Hess when it was first announced last October, and the FTC sent a second information request to Chevron ( CVX ) two months later.

Hess had communicated publicly and privately with members of the Organization of the Petroleum Exporting Countries (OPEC) group of oil producers, and encouraged high-level representatives of the group "in their stated mission to stabilize global oil markets," the FTC said on Monday

Allowing him to join Chevron's ( CVX ) board "would amplify Mr. Hess's supportive messaging to OPEC and others, thereby meaningfully increasing the likelihood that Chevron ( CVX ) would align its production with OPEC's output decisions to maintain higher prices," the FTC said.

A spokesperson for Hess did not immediately reply to a request for comment.

Exxon Mobil ( XOM ) and CNOOC Ltd, Hess's partners in a Guyana joint venture, are challenging the deal by claiming a right of first refusal to any sale of Hess's Guyana assets, the prize in the proposed merger.

A three-judge arbitration panel is due to consider the case next May. Chevron ( CVX ) and Hess say a decision is expected by August, while Exxon Mobil ( XOM ) expects it by September 2025.

John Hess will be allowed to advise Chevron ( CVX ) on discussions with Guyanese government officials, according to the FTC order.

The proposed all-stock acquisition is one of the largest in a consolidating U.S. oil and gas industry where several multibillion-dollar deals have been disclosed.