Ousted Catalan leader Carles Puigdemont has called for a united political front in the 21 December election to continue the drive for independence from Spain.
He also called for support in protest against the imprisonment of former members of the regional government.
Mr Puigdemont, who went to Belgium after his government was fired following a unilateral declaration of independence, said yesterday that he was considering standing in the election from Brussels.
In Spain's gravest political crisis since the return of democracy in the late 1970s, Prime Minister Mariano Rajoy called the snap election after taking control of Catalonia a week ago.
Political parties that wish to run on a common platform have until Tuesday to register any potential coalition, and until 18 November to put forward their candidates.
"It is time for all democrats to join together. For Catalonia, for the freedom of political prisoners and for the republic," Mr Puigdemont said in a tweet that included the hashtag llistaunitaria.cat, a site calling for parties to unite against the Spanish government at the ballot box.
Signatures on the website rose to over 40,000 from just 2,000 within a few hours of Mr Puigdemont's tweet.
És el moment que tots els demòcrates s'uneixin. Per Catalunya, per la llibertat dels #presospolitics i la República https://t.co/W4WDeUIB43 pic.twitter.com/FwbnA2wMQE
— Carles Puigdemont 🎗 (@KRLS) November 4, 2017
Last Thursday, nine members of Mr Puigdemont's sacked cabinet were ordered by Spain's High Court to be held on remand pending an investigation and potential trial.
One member of the dismissed cabinet, Santi Vila, was released after paying bail of €50,000 yesterday.
The other eight could remain in custody for up to four years.
Yesterday, Spain issued an arrest warrant for Mr Puigdemont and four associates to answer charges of rebellion, sedition, misuse of public funds, disobedience and breach of trust relating to their secessionist campaign.
Catalan civic groups Asamblea Nacional Catalana and Omnium Cultural - whose leaders were imprisoned last month on sedition charges - have called for a general strike on 8 November and a mass demonstration on 11 November to protest against the detentions.
Mr Puigdemont has said he would not return to Spain until he has been given unspecified "guarantees" by the Spanish government.
Following the warrant, any extradition process could take 45 days, though this could be extended up to 90 days.
Mr Puigdemont reiterated in a tweet that he would fully cooperate with Belgian justice following the warrant.
When asked if he would detain Mr Puigdemont, Belgian prosecutor Eric Van Der Sypt said it was unlikely.
He said: "Tomorrow, or it could be possible on Monday. We are not in a hurry.
"He said he would collaborate. We don't have any reason to believe he will flee. We are going to do this thoroughly."
While anti-independence parties urged Catalans to go out and vote in the December election, the arrests helped fuel the antagonism felt by many in the region toward the central government in Madrid.
"To pick someone up and arrest them is not politics. Politics is talking, discussing. To arrest some, it seems to me a little bit like a fascist government," said one Barcelona resident.
