Some 400,000 people aim to join hands along the entire coastline of the northeastern region of Catalonia to demand an historic redrawing of the map of Spain.
The protest is being organised by Catalan separatists on the region's national day, or Diada, which recalls the final defeat of Catalan troops by Spanish King Philip V's forces in 1714.
Although the event is tagged the "The Catalan Way Towards Independence", the route faces a major roadblock in the form of the Spanish government.
Prime Minister Mariano Rajoy's right-leaning administration refuses to countenance a breakup of Spain, and has vowed to block a referendum on self-rule that Catalan president Artur Mas has promised for 2014.
In a sign of its determination, Madrid called on the Constitutional Court to strike down the region's latest attempt to assert itself: a parliamentary declaration of sovereignty in January.
The court agreed to hear the case, meaning the declaration is suspended until it makes a ruling.
Proud of their distinct language and culture, yet suffering in Spain's recession, many of the 7.5 million people in debt-laden Catalonia resent seeing their taxes redistributed to other parts of the country.
Catalonia has a jobless rate of 23.85 percent — lower than the national average of 26.26 percent but still painfully high — and a public debt of €50.9 billion ($67 billion).
The region had to go cap in hand to Madrid in January to ask for €9.07 billion ($11.9 billion) from a fund to help debt-laden regions.
Hundreds of thousands of people joined in a huge national day rally last year as Catalan separatist stirrings were stoked by the cuts to health and education services.
Yet a year later their aspirations remain frustrated.
Just days before the Diada, Catalonia's political chief seemed to cast doubt on the 2014 referendum in a radio interview.
The 2014 poll would be organised respecting the law and with the agreement of Spanish government, Mas said, adding that such support was unlikely.
If Madrid refused to relent, Catalans could use regional government elections scheduled for 2016 as an alternative form of plebiscite, he argued.
But the next day Mas insisted that the 2014 referendum would go ahead "one way or the other".
Catalans, who have a reputation as impeccable organisers, say the human chain will pass through 86 cities, towns and villages over more than 400 km.
A total 350,000 people have so far signed up for the chain in Catalonia, according to the latest update by the organisers, the Catalan National Assembly.
About 5,000 volunteers will help run the protest. Some 1,500 buses will help move protesters into position.
Police will deploy 4,000 officers including in the regional capital Barcelona, where anti-independence protesters calling for Spanish unity are also seeking permission to rally.
Catalan activists say they are organising 110 smaller human chains in advance of , with rallies in Australia, Africa, Asia, including one at the Great Wall of China, and the Americas.
The protest is an attempt to emulate the 1989 Baltic Way chain that called for the independence of Estonia, Latvia and Lithuania during the breakup of the Soviet Union.
"There are big countries and small countries in the world, some industrialised and some not, and they all survive," said economics professor Antonio Argandona of the IESE Business School in Barcelona.
"So, can Catalonia survive? Yes, in the sense that it has a sufficiently solid economy to find its way," he said, warning however that it would still carry a price.
"It all depends on how a possible independence with Madrid is negotiated."
Mas has said he supports the protest but will not join in himself, out of respect for his role as political leader of all Catalans, including those that want to remain part of Spain.