Sinn Féin MEP Matt Carthy was the only Irish MEP to speak at the first meeting of the new European Parliament in Strasbourg on Tuesday, as he raised the exclusion of pro-independence Catalonia MEPs from the sitting.
Mr Carthy spoke on a point of order during the brief sitting, which was adjourned after less than half an hour.
“I want to congratulate all the MEPs who have been elected and who are here today,” Mr Carthy said.
"But unfortunately some MEPs who have been elected have been denied access to this House. Three representatives of the Catalan people have been denied representation in this House," he said, addressing the outgoing president of the parliament, Antonio Tajani.
“This House needs to stand up for democracy, needs to stand up for human rights,” Mr Carthy said.
"If this House doesn't value the votes of the people of Catalonia then the credibility of this House itself will be undermined. So I ask you today, Mr President, to make a statement on behalf of the elected MEPs of this institution and therefore reinforcing the value of democracy and human rights across Europe, " he said, to loud applause, including from a number of Irish MEPs sitting with him.
His Sinn Féin colleague Martina Anderson, one of the North's three MEPs who will sit until the UK leaves the EU, held up a picture of the Catalan independence leader Carles Puigdemont as Mr Carthy spoke.
Mr Puigdemont is one of three pro-independence MEPs elected in Catalonia in the recent European elections. However, the three have been prevented from taking their seats as the Spanish government has declined to include their names on the list of MEPs duly elected it is required to send to the parliament.
About 4,000 supporters of Catalan independence, many of whom had travelled from their homes, demonstrated outside the parliament on Tuesday.
New MEPs Clare Daly and Mick Wallace sat with Mr Carthy, wearing T-shirts emblazoned with an image of WikiLeaks founder Julian Assange.
In a tweet, Mr Wallace said that Mr Assange “is in prison because he exposed the ugliness of US Foreign Policy. Anyone who cares about a free independent media should challenge the treatment of Julian Assange.”
Mr Assange faces a hearing in the UK for extradition to the US on charges of leaking military secrets. He lived in the Ecuadorian embassy in London for seven years, taking refuge there after being accused of sexual assault offences in Sweden. Earlier this year, the Ecuadorian authorities revoked his asylum.