The vote, which has not been sanctioned by the Spanish government, has been met with fury by the EU.
But Hungary, a regular critic of EU interference, said today they back the independence vote and warned Brussels to back off.
A spokesman for Viktor Orban’s government said: “The will of the people is always what matters, that is the position.
“[The legality is] an internal issue for the Spanish and Catalan people.”
He said democracy means respecting “the will of the people” – something the EU needed to take note of.
The EU has inevitably waded into the row, talking down a hypothetical independent Catalonia before a vote has even taken place.
President of the European Parliament Antonio Tajani warned the new state “would start from scratch” with the EU – meaning the north-east Spanish region would automatically cease to be part of the bloc and would have to apply as a new state if it did achieve independence.
In an interview with El Periódico de Catalunya last week he said: “Catalonia would have to ask for the negotiation of a commercial agreement, access to the internal market.
“And then we would have to see how Europe would respond, including Spain.”
But he acknowledged people supported the Catalan independence cause, he stressed it was import not to “violate the constitution” in order to hold the vote.
Mr Tajani added: “Those are the rules.”
Jean-Claude Juncker has also hit out at the vote, echoing Mr Tajani’s warning Catalonia would start from scratch.
The president of the European Commission said: “If there were to be a ‘yes’ vote in favour of Catalan independence, then we will respect that opinion.
“But Catalonia will not be able to be an EU member state on the day after such a vote.
“If northern Luxembourg were to cede from the south, the same rules would apply.”
Catalonians will go to the polls on October 1. With just weeks to go the ‘Yes’ vote is leading by six points in the polls.
It comes amid a backdrop or constitutional chaos in Spain, after the Madrid government declared the referendum illegal. Those opposing the legality of the vote are planning to boycott the referendum.