The government asked the Constitutional Court on Wednesday to block the Catalan parliament from voting on a bill that lays the groundwork for the plebiscite.
Following are other legal tools which Madrid could use to stop the referendum:
Punishing public workers
Public workers who help stage the referendum face sanctions.
In most cases public workers could be temporarily suspended, or have their salary docked, said Yolanda Gomez, a constitutional law expert at Spain's distance-learning university UNED.
The sanctions could be slapped for example on university rectors or high school principals who open their schools on October 1 to be used as polling stations.
Depending on the seriousness of the offence, public workers and elected officials could face criminal charges or be ordered to pay compensation if a court rules that they diverted public funds to carry out the vote.
Suspension from public office
Spain's Constitutional Court can also fine or suspend public workers and elected officials who disrespect its rulings.
Prime Minister Mariano Rajoy's conservative government included this power in a 2015 legal reform which aims to ensure that the court's rulings are obeyed.
It would allow the court to target the head of the Catalan regional government, Carles Puigdemont, or the president of the Catalan parliament, Carme Forcadell, if they press ahead with the referendum.
Adela Asua, who was until recently the vice-president of the Constitutional Court, warned in an interview with Cadena Ser radio that the court must weigh very carefully what it does with this new power as it could lead to a "spiral of suspensions".
"It's not very comfortable for the court, that is obvious," she said.
Declare emergency
A 2015 law allows the government to declare by decree a temporary "situation of interest for national security" in a specific part of Spain.
The law allows the government to appoint an authority with "powers to direct and coordinate action" to resolve the crisis.
When the law was introduced, Rajoy said it would be an alternative to declaring a more serious "state of exception" or "state of siege".
The government could use this law to temporarily control Catalonia's regional police force, the Mossos d'Esquadra.
The law would make it possible alter the chain of command of the Mossos so that Interior Minister Juan Ignacio Zoido is in charge instead of the interior minister of the Catalan regional government, Joaquim Forn who back independence.
The government could then send local police "with the express order to close a place where voting is taking place," said Gomez.
The advantage of this measure is that it could be adopted "very quickly" by Spain's cabinet, said Gomez.
Suspending regional autonomy
Under Article 155 of the Spanish constitution, Madrid can directly intervene in the running of the region and force it to drop the vote which, potentially, would involve suspending the regional government's authority to rule.
The article allows the central government to "adopt the necessary measures" in a region to make it "forcibly comply" with the constitution or other laws.
It could be used by Madrid for example to order the closure of schools in the region to stop them being used as polling stations.
Invoking this article is considered a last resort. It would require the leader of the regional government to be summoned, and if he refuses, it would require the approval of the absolute majority of the Senate, Spain's upper house of parliament.
Using this tool would take more time than the other measures at the government's disposal.
It is the most unpopular and politically risky measure to use since "it has always been seen as removing a region of its legitimate powers", said Gomez.
The article has never been invoked since the adoption of Spain's 1978 constitution.
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