Wales’ First Minister Mark Drakeford has urged MPs to act quickly to make sure the next prime minister holds another referendum on EU membership.
He has written to all Welsh MPs, asking them to force the government to publish legislation by the end of July that would pave the way to a public vote.
A former Brexit minister said he was being “contemptuous” of democracy.
The winner of the Tory leadership race between Jeremy Hunt and Boris Johnson will be announced on July 23.
Mr Drakeford’s letter underlines growing differences between Welsh and UK Labour on Brexit.
After a poor showing for Labour at the European elections last month, Mr Drakeford said the time had come for a second referendum on whatever Brexit deal emerges between the UK and the EU.
In Westminster, however, Jeremy Corbyn’s team is still hammering out the party’s position.
On Wednesday, Labour MP Dame Margaret Becket told BBC Radio 4’s Today that unnamed people around Mr Corbyn wanted Britain out of the EU and “don’t give a toss” what party members think.
In his letter to MPs, Mr Drakeford said the Welsh Assembly had endorsed his position of wanting a second referendum and that the Welsh Government would campaign to remain in the EU.
He added it would be “outrageous” for the UK government to take the country out of the EU without a deal.
“I therefore urge you to continue to seek to legislate not just to prevent no deal, but also to force the government to bring forward a referendum bill by the 31st of July,” he wrote.
“This must be done quickly – we cannot afford the economic damage being done every single day as a result of Brexit uncertainty.”
Clwyd West MP David Jones, a former Brexit minister, said Mr Drakeford “appears unwilling to acknowledge Wales voted clearly to leave the EU in 2016”.
“It is disturbing that the first minister should be so apparently contemptuous of the democratic process,” he said.