Spain's conservative national government fiercely opposes independence for the rich northeastern region of Catalonia, which wants to follow Scotland's example by voting on its political future.
An alliance of pro-separatist parties want the regional vote to serve as a de facto referendum by running on a joint ticket, campaigning on the single issue of independence.
"If in this process, the Spanish state, through its political or legal decisions, blocks the autonomous government of Catalonia or the Catalan parliament, we will move forward with a declaration of independence," said Raul Romeva, a former MEP and key figure in the coalition, which brings together the centre-right CDC party and left-wing ERC.
"(We are) going for broke. We are betting everything on this, no turning back," he said at the presentation of the "Junts pel si" (Together for yes) list of candidates at the Museo de Historia de Catalunya.
The aim would be for a negotiating process to be concluded in 18 months, with institutions such as a taxation office set up.
The process would also pave the way for a binding independence referendum in 2016.
Spain's Justice Minister Rafael Catala told conservative daily ABC he would not rule out the suspension of regional autonomy if a separation process were to get underway, adding that Spain's constitution made provision for such a move.
"There will be no independence for Catalonia," Prime Minister Mariano Rajoy said on Thursday.
Catalonia, which is home to about 7.5 million people, has seen a rise in separatist sentiment at a time when its debts have forced local spending cuts and prompted renewed debate over how it is funded within Spain's regional structure.
Proud of their distinct language and culture, many Catalans say they get a raw deal from the way their taxes are redistributed to the rest of Spain.
The region accounts for a fifth of Spain's output and has an economy roughly the size of Portugal's.