Leaving the European Union would threaten cooperation in tackling climate change, Plaid Cymru has said.
In its European Parliament election manifesto, Plaid is calling on the EU to establish a deal that includes the aim of 100% self-sufficiency in renewable electricity by 2035.
The party is also calling on the EU to develop an investment fund from 2020 to help boost the Welsh economy.
Plaid is one of eight parties in Wales standing in the May 23 poll.
The anti-Brexit party is calling for a further referendum on Britain's relationship with the EU - as are the Liberal Democrats, Change UK and the Greens.
The party's leader Adam Price has said Wales should hold an independence referendum if Brexit happens without a further EU poll.
During its election campaign launch in Cardiff, Mr Price said Plaid was targeting Labour voters in particular who felt let down on Brexit.
All countries in the EU have committed to ensure that young people under the age of 25 receive an offer of employment, continued education, apprenticeship or traineeship within four months of becoming unemployed or leaving formal education.
One of Plaid's manifesto pledges is to work towards full implementation of the EU's Youth Guarantee scheme.
Plaid is also pledging to create a Welsh Migration System if it is in government in Wales, but the party is currently in opposition in the Welsh Assembly, and migration policy is the UK Government's responsibility.
Mr Price, the Carmarthen East and Dinefwr AM, launched Plaid's election manifesto on a farm visit near Caernarfon on Monday, with the party's lead European candidate and sitting MEP Jill Evans.
Ahead of the visit, Mr Price said: "Westminster is broken, and Wales deserves better.
"The manifesto we're launching today is a manifesto to make Wales matter.
"The truth is that while the EU has invested in Wales' communities, it's Westminster that has let us down time and time again.
"That is why we're appealing for support from across the political spectrum: to secure a People's Vote, to make Wales matter, and ultimately to maintain Wales' membership of the EU," he added.
The European Parliament elections in Wales
There are eight parties fighting for four Welsh seats in the European elections on 23 May.
Welsh Labour, the Welsh Conservatives, Plaid Cymru, the Welsh Liberal Democrats, UKIP and the Green Party are joined by Change UK and the Brexit Party.