His move could deepen the confrontation between Madrid and the northeastern region but also signals a way out of Spain’s biggest political crisis since a failed military coup in 1981.
Rajoy would probably call a snap regional election after activating Article 155 of the constitution that would allow him to sack the Catalan regional government.
Catalan leader Carles Puigdemont issued a symbolic declaration of independence from Spain on Tuesday night but then immediately suspended it and called for negotiations with the Madrid government.
"The cabinet has agreed this morning to formally request the Catalan government to confirm whether it has declared the independence of Catalonia, regardless of the deliberate confusion created over its implementation,” Rajoy said in a televised address after a cabinet meeting called to consider the government’s response.
He later told Spain’s parliament the Catalan government had until Monday, Oct. 16 at 0800 GMT to answer. If Puigdemont was to confirm he did declare independence, he would be given an additional three days to rectify it, until Thursday, Oct. 19 at 0800 GMT. Failing this, Article 155 would be triggered.
It is not yet clear if the Catalan government will answer the requirement but it now faces a conundrum, analysts say.
If Puigdemont says he did proclaim independence, the central government will step in. If he says he did not declare it, then far-left party CUP would probably withdraw its support for his minority government.
"Rajoy has two objectives: if Puigdemont remains ambiguous, the pro-independence movement will get more fragmented; if Puigdemont insists on defending independence then Rajoy will be able to apply Article 155,” said Antonio Barroso, deputy director of the London-based research firm Teneo Intelligence.
"Either way, Rajoy’s aim would be to first restore the rule of law in Catalonia and this could at some point lead to early elections in the region.”
The stakes are high - losing Catalonia, which has its own language and culture, would deprive Spain of a fifth of its economic output and more than a quarter of exports.