A delay to Brexit agreed by the European Union should be used to secure a referendum, Plaid Cymru has said.
Plaid Cymru's Liz Saville Roberts called for opposition parties to untie to deliver a further public vote on the UK's status in the EU.
But colleagues in the Liberal Democrats and the SNP have instead called for an election, on December 9.
MPs will vote later on the government's own calls for an election on 12 December.
First Minister and Welsh Labour leader Mark Drakeford welcomed the extension.
"Now is the time to take the decision back to the people, with an option to remain in the EU on the ballot paper," he tweeted.
Plaid Cymru's four MPs have worked with others in the opposition opposed to Brexit or leaving without a deal. The comments of Plaid's Westminster leader suggest opinions on tactics have diverged.
It comes after Gower Labour MP Tonia Antoniazzi said she did not think Jeremy Corbyn can win an election while Brexit is causing political "disarray".
The president of the EU council, Donald Tusk, announced that the leaders of the remaining 27 states in the union and agreed to a "flextension" of up to 31 January next year.
That means the UK could leave earlier if it ratifies Boris Johnson's Brexit deal before then.
Ms Saville Roberts said: "Those of us opposed to inflicting the harm of Brexit on the four nations of the UK must now unite again to deliver the most sensible way to end this mess - a final say referendum.
"The extension granted by the EU should now be used to secure a People's Vote and end the Brexit chaos.
"If the Government fail to deliver this, opposition parties must work together, and if necessary, form a caretaker government to deliver this most democratic solution to Brexit."