Plaid Cymru has launched a campaign to establish Welsh as an official language of the European Union.
Jill Evans is leading the campaign to make Welsh an offical EU language
The party wants its MEPs to be able to use Welsh in European parliamentary proceedings in Brussels and Strasbourg.
It is calling for the proposed European constitution to be translated into Welsh before it will consider supporting a referendum.
Plaid's Jill Evans, the party's leader in the European Parliament, is spearheading the campaign.
The policy was approved at the party's annual conference in Llandudno.
It said that if Welsh was adopted as a formal EU language, it would mean that Welsh speakers could write to European institutions and expect a reply in their language.
It would also mean that Welsh speaking MEPs would be able to talk in Welsh during formal proceedings, with what they say being simultaneously translated into the other official EU languages.
Plaid has been prompted to put Welsh back on its European agenda following Ireland's request for Irish to become an official language.
The Spanish government is also making the same demands for Catalan, Basque and Galician.
Jill Evans MEP said the party's campaign aimed to put pressure on the UK Government to negotiate the necessary changes.
She said: "It is a matter of principle for us that Welsh should be treated equally with the languages of other European countries.
Plaid Cymru wants to be able to use Welsh in the European Parliament
"The European Union is funded through public money and should be there to serve all of the people - it should have a duty to provide services to Welsh speakers in their language of choice.
"We're now seeing similar moves for Irish, Catalan and Basque to get this status.
If it's good enough for them, then why not Welsh?"
Ms Evans pointed out that Maltese already has official status - Malta was one of the ten countries admitted to the EU in May 2004 - even though fewer people speak the language than speak Welsh.
She added that having Welsh as an official EU language would also boost tourism.