Spain's government is seeing if it can bring criminal charges against the speaker of the Catalan parliament for letting the assembly vote for independence.
Politicians in Barcelona, the capital of Catalonia, voted on Wednesday to continue with a plan to detach the north-eastern region from Spain.
On Friday, Soraya Saenz de Santamaria, deputy prime minister in the caretaker administration in Madrid, said the government had asked the Constitutional Court to annul Wednesday's resolution and see if Catalan assembly speaker Carme Forcadell had broken the law by trying to press ahead with the independence plans.
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The text passed by the Catalan parliament outlines the steps Catalonia - a region of 7.5 million people which represents nearly a fifth of Spain's economic output - needs to take to defend its right to self-determination.
It argues the "only way possible" for Catalans to exercise their right to decide on their future is if the region "disconnects" from the Spanish state and disobeys Spanish institutions.
"It's a violation of our constitution," government spokeswoman Santamaria told reporters in Madrid after a cabinet meeting.
She also warned that separatist politicians, and especially Forcadell, the speaker, risked fines of up to 30,000 euros ($33,500), suspension from their posts and even legal action if they continued to disobey Madrid.
Speaking to a Catalan television channel, Forcadell hit back at Madrid's reaction, accusing the government of using legal tools to try and fix something "they do not know how to resolve politically.
"This does not help resolve the problem, it makes it worse," she said.
With the backing of acting Prime Minister Mariano Rajoy's conservative government, Spain's Constitutional Court has already taken measures against Catalonia's independence drive.
It suspended an independence referendum called by the Catalan government in 2014, as well as a resolution passed by Catalonia's parliament in November declaring the start of a secession process.
Secessionist parties hold a majority in the 135-seat Catalan parliament, and the text was approved with 72 votes in favour.
A poll published last week showed support for Catalan independence growing at a time when political deadlock at the national level after two inconclusive general elections has prevented the formation of a new government in Madrid.
The survey, by the regional government's official pollster, found 47.7 percent of Catalans supported independence, with 42.4 against.
Many Catalans who favour breaking away from Spain say their region pays too much in taxes and receives less than its fair share of government investment. Independence also sentiment grew during Spain's near economic meltdown during the financial crisis.