In what will further escalate tensions between Madrid and separatist authorities in Catalonia, lawmakers from the ruling, pro-independence coalition in the northeastern region unveiled a bill that lays out the steps to split from Spain.
The bill "provides a legal framework for the period immediately after" a possible victory of the "yes" side in the referendum, said Lluis Corominas, head of the parliamentary group of the "Together for Yes" coalition.
It will be approved next month by Catalonia's majority separatist parliament, and automatically applied if the "yes" vote wins. Catalonia, a wealthy region of 7.5 million inhabitants with its own language and customs, has long demanded greater autonomy.
For years separatist politicians in the region have tried to win approval from Spain's central government to hold a vote similar to Scotland's 2014 independence referendum from Britain -- which was approved by London -- and resulted in a "no" vote.
But Madrid has remained steadfast in its opposition to such a vote, considering it a threat to Spain's unity.
The Constitutional Court has warned Catalonia's elected officials that they will face legal consequences if they take any steps towards holding such a vote.
But they have pressed ahead undeterred.
Among other things, the bill states that if the "yes" side wins, "Catalonia has all sovereignty rights... where its continental platform and exclusive economic zone are concerned."
This it defines as all of its land territory including the subsoil, its own waters "including the seabed and subsoil" and the region's airspace.
Asked how it would take control of its borders given Madrid's rejection of a referendum it deems illegal, Corominas and other separatist lawmakers present at the press conference were unable to give further details.
If the "no" wins, though, fresh regional elections will be held, they said.
Catalans are divided over the issue of independence, with 41.1 percent in favour and 49.4 percent against, according to the last government poll.
A large majority, however, wants a referendum to take place to settle the matter.