The Spanish Finance Ministry issued a statement on Monday reminding taxpayers in Catalonia that criminal prosecution may ensue if taxes were not paid on time to the correct revenue collector, which for companies and the self-employed across Spain who pay VAT, corporation tax and income tax means the state.

Earlier on Monday, Catalan First Minister Carles Puigdemont (Junts Pel Sí, "Together For Yes") announced that a newer, updated version of the Catalan Tax Agency was ready to do business and prepared for whatever happens after the illegal independence referendum on October 1. "We're ready!", he tweeted.

Deputy First Minister Oriol Junqueras (Esquerra, ERC) replied to his boss that the agency was ready "to become the key piece of the tax system" and collect €42 billion in revenue.

The secession bill presented last week—which has already been tabled in the Catalan regional parliament—includes plans for taking control of tax revenues in the region.

Regional tax authorities in Spain are allowed to collect some revenues, from inheritance or wealth taxes, for example, but the bulk of ordinary taxes—income tax, VAT, corporation tax, etc.—are still the responsibility of the state.

In its statement on Monday, the Finance Ministry said taxes are only considered paid if the money is sent to the right agency. If they are not, they will be considered unpaid, leaving taxpayers liable to inspection, fines and possible criminal prosecution.

Companies are not off the hook and the ministry noted company directors could be prosecuted for fraudulent tax behaviour.

Under Spanish tax laws, late payment of VAT is considered an administrative problem, up to a point, but late- or non-payment of quarterly employee income tax contributions theft.

While Catalonia had created its own tax agency in 2007, said the ministry, the Constitutional Court had recently struck down provisions in a new regional law that were unconstitutional or otherwise illegal.

During a press conference on Monday, Spanish Prime Minister Mariano Rajoy said "the referendum is absurd and a con".

Catalan First Minister Puigdemont replied later in the day: "forbidding ballot boxes would be a coup [d'état]".