Plaid Cymru leader Adam Price will say no party has a “higher ambition for Wales” when its general election campaign is launched on Monday.
Mr Price is expected to tell the launch in Menai Bridge, Anglesey, that Wales is being “held back by Westminster”.
Plaid is aiming to increase its tally of four MPs won in 2017, with Ynys Mon a top target.
The party wants another referendum on Brexit in which it would campaign for the UK to remain in the EU.
In September, Mr Price called for his party to go into a snap poll promising to cancel Brexit without the need for a further referendum, but party members voted to support another vote on membership unless there is a prospect of a no-deal Brexit.
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Could there be a remain alliance?
In August, Plaid Cymru did not field a candidate in the Brecon and Radnorshire by-election after entering a pact with the Liberal Democrats and Green Party to avoid splitting the remain vote. The seat was won by Lib Dem Jane Dodds,
Despite reports they have reached a wider electoral pact for the election on 12 December, Plaid sources said the discussions within and between the parties continue.
The party won four seats in the 2017 election, but won by slender margins of 104 in Ceredigion and 92 in Arfon, while 16 of its 40 candidates lost their deposits after failing to secure 5% of the constituency votes.
But, Plaid came second in May’s European elections in Wales and beat Labour in a Wales-wide election for the first time.
What is Plaid promising?
The party is campaigning for a “Welsh green jobs revolution”, the creation of a Welsh justice system, which includes the transfer of policing powers to Cardiff and £50m to recruit 1,600 new police officers.
Other pledges announced ahead of the launch relate to issues that are the responsibility of the Welsh Government – social care, childcare and building affordable homes.
Asked whether the party was deliberately confusing matters, a Plaid Cymru source said: “Many of the issues are decided in Westminster or their funding allocated there.
“The sad fact of the matter, however, is the media still does not understand devolution, so we have to talk about the whole range of issues that matter to people’s lives.”
Mr Price is expected to tell the launch: “Plaid Cymru’s ambition for Wales is without limit. We know the potential of our country. We know what we can achieve. And Plaid Cymru will always demand more for Wales.
“But the truth is Wales is being held back by Westminster. We’re at the bottom of every league table going.
“It is now beyond doubt that it’s time for change.”