As Civil Guard officers visited the pro-independence newspaper Vilaweb on Friday, its editor, Vicent Partal, was interviewing Catalan First Minister Carles Puigdemont at his office. "It seems like the Spanish government has almost deployed Articles 116 and 155 without having to decree them", he told the journalist.

Article 116 describes how the states of alarm, exception and siege work in Spain.

Referring to an announcement by Spanish Finance Minister Cristóbal Montoro on Friday morning, Mr. Puigdemont's Deputy First Minister, Oriol Junqueras, said during a rally on Friday night that "taking control of Catalan government accounts is a concealed way of liquidating the country's institutions and a concealed way of applying Article 155 of the Constitution".

Also in Barcelona on Friday, Spanish Prime Minister Mariano Rajoy made televised remarks to members of the Popular Party in Catalonia. One phrase towards the end of a typically rambling Rajoy speech has political journalists in Spain wondering if he will use Article 155 this time. "You", he said, referring to Catalan separatists: "are making a mistake and you are going to force us to go where we don't want to go".

El País used that phrase as its front page headline on Saturday. "Where we don't want to go" is being interpreted as a veiled reference to Article 155 of the Spanish Constitution. But what, exactly, is it?

Two years ago in 2015, Spain's then Foreign Secretary, José Manuel García Margallo (Popular Party) said during a TV interview that dusting off Article 155 would be politically explosive in Spain: "It is obvious that there is a [possible] legal reaction, which is suspending home rule, but that is an atomic bomb".

Article 155 of the Spanish Constitution outlines how the central government in Madrid would suspend home rule or regional government in one of Spain's 17 autonomous communities. It has never been used and only contains the following two points.

"1. If an autonomous community [Spanish region] were not to fulfil the duties imposed upon it under the Constitution or other laws, or were to act in a manner that gravely attacked the general interest of Spain, the government, having first notified the First Minister of the autonomous community and, in if no reply were received, with an absolute majority in the Senate, may adopt the measures necessary to oblige that [region] to forcibly comply with said duties or to protect the aforementioned general interest."

"2. To execute the measures foreseen in the previous section, the government may give instructions to all of the authorities in the autonomous communities."

The Spanish Congress's legal synopsis of the article describes it as an "exceptional or extreme" measure "for situations that are equally exceptional or extreme".

That, along with a reading of the relevant Senate rules, leads to a seven-point implementation process to watch out for over the next few days, if Madrid decides to try to use it.

  1. Madrid formally notifies Puigdemont: the central government must send some sort of formal notification to the Catalan government attempting to make the First Minister, Carles Puigdemont, comply with whatever duties or laws the central government believes he is not complying with;
  2. Puigdemont rejects the formal notification: how the Catalan leader's rejection of or non-compliance with Madrid's summons might be proven is not clear;
  3. Government petitions Senate: the central government must present the formal notification, the proof of its rejection and the measures it wishes to implement before the Speaker of the Senate;
  4. General Commission of Autonomous Communities: The file gets sent to the Senate commission that deals with the Spanish regions. It is currently made up of 54 senators: 30 Popular Party, 12 Socialist Party, 4 Podemos, 8 minority parties.
  5. Senate notifies Puigdemont: The Senate commission would ask the Catalan First Minister to provide the data and allegations he believed relevant to his position. He could also choose to appoint a representative before the Senate;
  6. Commission draws up proposal for debate: and makes a recommendation based on the government's petition; the commission may suggest modifications;
  7. Senate debates proposal and takes a vote. An overall majority is required to pass the motion: 134 out of a total of 266 senators. The governing Popular Party, with 149 senators, holds a comfortable overall majority of 16 in Spain's upper house;

The Speaker of the Spanish Senate is currently Pío García-Escudero (Popular Party). The autonomous communities commission is currently chaired by Juan José Imbroda Ortiz (Popular Party), who is also the First Minister of the Spanish North African city of Melilla. The PP holds a comfortable majority in the Senate overall and on the autonomous communities commission.

Earlier this week, Spanish news agency Europa Press reported that an unnamed government source had told them the Article 155 process could be completed "in five days". 24 hours would be enough time, according to the source, to formally notify Mr. Puigdemont and give him a last chance to comply.

If that is true, the Spanish government still has enough time to try to activate the article before October 1, when Catalan separatists mean to vote.

On Saturday, Mr. Puigdemont and his government met with the Mayor of Barcelona, Ada Colau, and 700 other separatist municipal leaders in the Plaza de Sant Jaume in central Barcelona, home to both Barcelona City Hall and the Catalan government. Outside, thousands of supporters had gathered and separatist flags waved in the sun. The Catalan anthem Els Segadors was sung several times. "We will vote! We will vote!", they chanted.

Updated: With correct figures for the members of the General Commission of Autonomous Communities.