PARIS (Reuters) – French President Emmanuel Macron told Britain’s Theresa May in a telephone call on Friday that the deal she negotiated over Britain’s departure from the European Union was the “best one possible”, an official in the French presidency said.

The future of May’s agreement hangs in the balance in the run-up to a parliamentary vote, and calls for a second referendum – which she has consistently rejected – are growing. Opponents of the deal argue it could leave Britain trapped inside the EU’s customs union indefinitely.

“The president reaffirmed his support for the deal reached on Nov. 25, which is the best possible agreement for all sides,” the Elysee Palace official said.