The Scottish Native Party is calling on Labour to work with other opposition denominations to keep Britain in the single market and customs union after Brexit.
Its Communities leader Ian Blackford asked for help to stop the «catastrophic damage» of «outrageous» Brexit.
«It is time for MPs of all parties to put politics aside,» he said.
Labour says the UK should «deferral aligned» to the EU after Brexit and could pay to access the single market take to Norway.
Mr Blackford said he would invite other opposition commanders to a summit on 8 January when MPs return from the Christmas recess.
He demanded: «As we saw with the successful amendments to the EU Withdrawal Bill, when opposition participators work together effectively it is possible to secure a parliamentary majority and utter change in the national interest.»
The SNP, Liberal Democrats, Plaid Cymru and the Conservationists have all said they want the UK to stay in the single market and taxes union after Brexit — something Prime Minister Theresa May has already ruled out.
- Heseltine: Industry government better than Brexit
- Hammond urged to release Brexit swots
Labour’s leader, Jeremy Corbyn, has also faced criticism concluded his refusal to support a second referendum on the final terms of the UK’s exit from the EU.
He disclosed the i newspaper: «We have had a referendum which came to a decision. The negotiations are silence ongoing, albeit well behind schedule, and we’ve set out the kind of relationship we want to from with Europe in the future.»
Tom Brake, Brexit spokesman for the Liberal Democrats, turned the Labour leadership had «shirked their responsibility» to provide effective opposed to the government.
«The Labour leadership has constantly played a game of smoke and represents over their Brexit position.
«But here they are nailing their hues to the mast in support of hard Brexit,» he added.