The secret document includes a plan for the region to unilaterally break away from Spain should its citizens be prevented from holding a referendum on independence in the autumn.
The leaked plans provoked fury in Madrid.
Spanish Prime Minister Mariano Rajoy said: “This proposal is an unacceptable attempt to blackmail the state.”
He warned that oppening negotiations with Catalonia would go against Spain’s “constitutional order” and dismissed he latest formal request for a referendum by regional President Carles Puigdemont as “political, juridical and social nonsense”.
The Catalan government has promised electors a vote this autumn but Madrid has vowed to prevent it by any means necessary.
But in a letter to Mr Puigdemont the prime minister said: “I consider it inexcusable to have to reiterate to you not only the impossibility of taking part in what you propose but also the impossibility for your Government to raise such a grave threat to coexistence and constitutional order.”
Defence minister María Dolores de Cospedal likened the plot to a coup d’état.
Madrid steadfastly continues to refuse to even entertain the idea of allowing a referendum on Catalan independence even though most surveys show around 80 per cent of Catalans, including many unionists, would like the chance to vote.
Catalan independence would mean the loss of up to 30 per cent of Spain’s gross domestic product and Minister of the Economy Luis de Guindos insisted that is something the government “will never let happen”.
But at the same time, Catalonia’s regional government seems determined to stage a showdown with Mr Rajoy in Madrid.
The PM’s staunch defence of the country’s territorial unity is a vital vote winner for its core supporters.
And with corruption scandals engulfing senior members of his People’s Party breaking every week or two they are votes he cannot afford to lose.
Analysts fear prospects of a solution acceptable to both sides being found in the coming months are very slim but say it remains very doubtful that Spain – the eurozone’s fourth largest economy – will break up.