Remain-supporting parties
should discuss working together in a snap general election or second EU
referendum, Plaid Cymru's leader said.
Adam Price has written to the
Liberal Democrats, Green Party, Change UK and the SNP.
He said they should work together
for "as long as necessary" to deliver another vote on EU membership.
His call comes after the Brexit Party took two Welsh seats in
the recent EU elections.
Plaid Cymru and Labour each took
one of the country's four MEP seats in Brussels.
Despite the Brexit Party's
victory, Mr Price said the combined total votes given to anti-Brexit parties
shows that Brexit "cannot be considered the settled will of the
people".
The Brexit Party gained 32.5% of
the vote in Wales with UKIP taking 3.3% while Plaid Cymru received 19.6%, the
Liberal Democrats 13.6%, Green Party 6.3% and Change UK 2.9%.
"With the Brexit Party
having won the highest number of seats, there is now a grave risk that the
result will be used to justify a no-deal Brexit," Mr Price said.
"I am particularly concerned
that it will be used to influence the candidates running to become the next
leader of the Conservative Party."
He described an "urgent
need" for the parties to work together to "ensure that all the
nations of these islands are not dragged headfirst towards a no deal Brexit for
which there is no mandate".
Mr Price added: "We are
passionately pro-European parties who believe that our nations' rightful place
is at the heart of Europe.
"We must not let the
politics of the Brexit Party divide us as we seek to maintain our nations'
place in Europe."
Mr Price invited fellow leaders
to meet him for an "initial, exploratory" discussion.
A Welsh Liberal Democrat spokesman said the party was always happy to discuss ways of achieving "our
common aims".
He added: "Since June 2016, Liberal Democrats have led efforts in Parliament
to secure a people's vote, and this has included work with other parties with
varying degrees of success.
"We've done this because Remainers expect us to work together
where necessary to deliver a People's Vote."
Change UK MP Chris Leslie said the
party remains ready to continue working with other parties, including Plaid, to
"prevent a disastrous no-deal Brexit".
He added that Change UK has "already engaged in an unprecedented
level of cross-party cooperation since we formed".
The Green Party and the SNP have
been asked to comment.