Mariano Rajoy said if Catalan president Carles Puigdemont's response is that he indeed has formally proclaimed independence, he will have a few more days to drop the implementation of the declaration.
He later told Spain's parliament the Catalan Government had until Monday morning to answer.
Mr Rajoy also called the referendum, which had been ruled illegal, part of a strategy "to impose independence that few want and is good for nobody", saying it had led to "one of the most hard times in our recent history".
If Mr Puigdemont was to confirm he did declare independence, he would be given an additional three days to rectify it. Failing this, Article 155 would be triggered.
If Mr Puigdemont says he did not declare it, then far-left party CUP would likely withdraw its support to his minority government.
It is not yet clear if the Catalan government will answer the requirement but it now faces a conundrum, analysts say.
The EU and most of its 28 nations have not backed Catalonia's independence movement.
In a highly anticipated speech, Mr Puigdemont had said the landslide victory in the disputed referendum on 1 October gave his government in the regional capital, Barcelona, the grounds to implement its long-held desire to break its century-old ties with Spain.
The central government in Madrid responded to say it did not accept the declaration and did not consider the referendum or its results to be valid. Central authorities in Madrid had declared the referendum illegal and most opponents of independence boycotted it, reducing turnout to around 43 per cent.
"Neither Mr. Puigdemont nor anyone else can claim, without returning to legality and democracy, to impose mediation ..." However, he said he wanted to delay the action for several weeks to allow for possible discussions with the government.
When asked for a statement regarding Rajoy's statement, Catalan government spokesman Jordi Turull said that should Madrid invoke Article 155, the Catalan government would press on with its independence.
The political deadlock has plunged Spain into its deepest political crisis in more than four decades, since democratic rule was restored following the dictatorship of General Francisco Franco.
"We have given up absolutely nothing ..."
He said a deal was reached with Mr Rajoy to open talks in six months on reforming the constitution that would allow changes to the current setup governing Spain's 17 regions, including Catalonia.
Puigdemont's speech also disappointed supporters of independence, thousands of whom watched proceedings on giant screens outside parliament before sadly leaving for home.