Sinn Fein held an 'emergency solidarity rally' on Sunday evening to send a message of support to the people of Catalonia after the region attempted to vote in an independence referendum.
The referendum had been declared illegal by the Spanish government.
Almost 900 people were injured amid attempts by police to stop the vote from going ahead.
Derry's historic walls were lit up in the colour of the flag of Catalonia on Sunday night.
Sinn Fein MEP lead a delegation of more than 25 people to witness the vote in Barcelona.
"No one could have failed to have been impressed by the determination, defiance and dignity of the Catalan people during yesterday's referendum despite the repression they faced at the hands of the Spanish authorities," said Ms. Anderson.
"Young and old went to the polls to attempt to express their democratic rights, with some queuing for hours to do so despite repeated obstacles being placed in their way.
"In doing so they faced attacks, brutality and repression from the Spanish police in scenes that have no place in a modern democracy. But the Catalan people remained dignified and resolved that they would not be denied their fundamental democratic right."
Ms. Anderson added: "Their commitment to democracy was witnessed around the world on social media, as were the shameful actions of the Spanish authorities who tried to attack the very principle of democracy.
"In particular, I would like to pay tribute to the actions of the Catalan firefighters who lived up to their stated aim of protecting communities when they formed human shields around voters who were simply trying to have their voice heard.
"There is now an onus on the international community, and the EU in particular, to stand by the Catalan people, recognise their democratic vote and the outcome of the referendum.
"The EU must also challenge the use of violence against people attempting to express their democratic rights."