Plaid Cymru will rally support before an expected May general election by unveiling a "people's contract" at its spring conference.
Plaid president Dafydd Iwan and assembly leader Ieuan Wyn Jones
All candidates will sign up to a pledge "based on socialist values and designed for the people of Wales".
Plaid, with four of Wales' 40 MPs, claimed it was now the socialist party in Wales and accused "New Labour in Wales" of "regurgitating London spin".
Plaid meets on Saturday at the Galeri enterprise centre in Caernarfon.
It is widely thought that the election will be in early May, and Plaid will focus its fire on the record of Labour governments in both Westminster and Cardiff Bay.
The party will hope to attract what party president Dafydd Iwan described as "traditional Labour voters... left feeling completely disillusioned with their party".
But Plaid will also seek to shore up its support in its northern and western heartlands, and has identified Ynys Mon as its main target seat.
Ieuan Wyn Jones was Ynys Mon's MP until 2001. He stood down to concentrate on his role as an assembly member. But Plaid lost the parliamentary seat by 800 votes and will be anxious to win it back.
The "people's contract" was described by Plaid as its "socialist antidote to New Labour".
Plaid parliamentary leader Elfyn Llwyd, MP for Meirionnydd Nant Conwy, said: "When people on the doorstep ask our candidates what they get if they vote Plaid Cymru at the general election, we will show them the people's contract.
"The contract makes it clear that when you elect a Plaid Cymru candidate you elect someone who is going to put Wales' interests first and never give in to the London agenda."
Caernarfon MP Hywel Williams said: "People are left feeling unsure of what exactly MPs do once they get to Westminster.
"The people's contract explains what Plaid MPs have done over the years. That is, we've stuck to a firm set of principles."
Plaid will also continue to attack Labour on Iraq, and will claim Wales should have a "proper parliament" by increasing the powers of the Welsh assembly.