A minister in the British government stepped down Friday to protest Prime Minister Theresa May’s Brexit plan and is backing calls for a second referendum on whether the country should leave the European Union.

Jo Johnson, younger brother of former Foreign Secretary Boris Johnson, said the withdrawal agreement being discussed by EU and British leaders would greatly weaken Britain and require the country to follow EU rules without having any say. The only alternative on the table, he said, is a no-deal Brexit that would “inflict untold damage” on Britain.

“It has become increasingly clear to me that the withdrawal agreement, which is being finalized in Brussels and Whitehall even as I write, will be a terrible mistake,” said Johnson, who was a transport minister in the government.

He said it would be proper to give the British public a chance to vote again because of the way the Brexit negotiations have evolved.

“Given that the reality of Brexit has turned out to be so far from what was once promised, the democratic thing to do is to give the public the final say,” he said.

His older brother Boris resigned in July to protest May’s Brexit plan — but Boris did so as a staunch support of a hard-line Brexit, while Jo Johnson backed the “remain” side during the June, 2016 referendum.

Jo Johnson’s resignation, and his call for a fresh referendum to test voter sentiment, further complicates matters for May as she tries to strike a deal with EU leaders that would pass muster with her own cabinet and win backing in Parliament.

She has consistently rejected the idea of another nationwide vote on Brexit, insisting her obligation is to make good on the will of the people as expressed in 2016.

Her Conservative Party remains deeply divided on her approach, and it is not clear if she will win wide backing from opposition Labour Party lawmakers when any proposed deal is put to Parliament.

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