The group, Europe for Ireland, has organised tickets with Ryanair for people to travel to Dublin next week.
They can fly on either Tuesday, Wednesday or on Thursday, the eve of the referendum, and return whenever they wish.
An email to their members says: “Europe for Ireland has arranged free flights with Ryanair from Charleroi to Dublin. You could take either of two daily flights on whichever day suits you and come back whenever you like. Even if you can manage to take just one day off, you could fly over and back on the same day.
“Europe for Ireland will arrange your booking. You don’t pay, you just turn up,” it adds.
Europe for Ireland is a group of Irish people living in Brussels and all over Europe who came together to promote a Yes vote to the Lisbon Treaty.
Their chairperson, Kevin Leydon, said they are encouraging people who have first-hand experience of working with and for the EU to share this experience with their relatives and friends at home.
“We are very happy with the response,” he added.
They had received a lot of support through their website also, including donations from individuals. They were looking for €15,000 to pay for operating costs and more substantial sums to pay foradverts.
The organisation ran into controversy recently when an Irish consultant sent out an email to EU lobby groups requesting donations on behalf of Europe for Ireland. He said the situation was “truly an emergency” and said the future of the EU was at stake.
Jim Murray, spokesman for Europe for Ireland, said they had not seen the email before it was sent out and they did not agree with his views.