With Catalan separatists contemplating whether to declare independence for the autonomous region, experts have detailed how the national government could react as tensions in the region rise.

The illegal October 1 referendum recorded 90 percent of Catalans voting in favor of independence, yet under half of the population voted, according to the Catalonia government. Meanwhile, Spain’s Prime Minister Mariano Rajoy denounced that a referendum had even occurred.

Here, CNBC outlines the options that the Spanish government could take if Catalonia declares independence:

Invoking article 155, which has never been used before, would allow the Spanish central government in Madrid to take away Catalonia’s autonomy, either partially or totally.

The article can be enacted if an autonomous community did not follow the laws under the Constitution or acted “in a manner that gravely attacked the general interest of Spain.”

It would take a few days for this process to occur, as Rajoy would have to formally notify Catalan President Carles Puigdemont and the Catalan government, and then put it up for a vote in the Senate if Puigdemont were to reject the notification. As Rajoy’s party represents a majority in the Senate, the article would most likely pass.

Once enacted, the entire Catalan parliament, made up of 135 members, would be dissolved and new regional elections would have to occur within the next two months, explained Marina Díaz Cristóbal, a professor of history and political science in Barcelona. Members of the current parliament could run again if they were not involved in illegal activities, she added.

“The risks of taking this road would be exacerbating the (pro-independence) movement,” said Cristóbal.

Also, there is nothing preventing Catalonians from simply electing another extreme pro-separatist as president.

The Spanish government could use the military to take direct control of the Catalan region. This option would be “very unlikely”, said Cristóbal, especially in the wake of the police violence towards Catalan citizens that occurred last week, which prompted a general strike on Tuesday.

If the Spanish government were to declare a state of emergency, it could perform actions that it normally could not under the Constitution in order to regain control over the Catalonia region.

Similar to martial law, the government would most likely have to bring in the national police to enforce the decision.

Rajoy has been clear that he will not discuss the illegal referendum, which seems to put negotiations with the Catalan government off the table.

The two leaders could accept the mediation of a third party so a new relationship between Catalonia and Spain could be established, said Cristóbal, possibly through a constitutional change.

Puigdemont has turned to the European Commission, the executive arm of the EU, for help, pleading for “international mediation” last week. However, the EU is standing behind Rajoy and calling the situation an internal conflict.

Without any backing from other countries, Puigdemont’s declaration of independence would be nothing but symbolic. However, the Spanish government would be forced to react to the statement to put the longstanding debate to rest.

Puigdemont has said he will address the regional parliament on Tuesday evening and it’s still uncertain whether he will go ahead with declaring independence — as he stated last week — particularly after a strong show of support in favor of unity with Spain.