The country is in the midst of its worst political crisis in a generation after separatists in the wealthy northeastern region voted in a banned referendum on October 1st to split from Spain.
Prime Minister Mariano Rajoy and King Felipe VI are due to attend a traditional military parade in central Madrid, where Spanish flags have been tied to balconies and windows around the city by pro-unity supporters on the nationwide holiday.
Armed forces will march down Madrid's Paseo de la Castellana boulevard to mark the day that Christopher Columbus first arrived in the Americas in 1492 while a pro-unity rally by members of the far-right is expected in the Catalan capital Barcelona.
Rajoy has vowed to do everything in his power to prevent Catalan secession and his government said Wednesday that it would take control of the region if it insisted on breaking away.
The warning came after Catalonia's president Carles Puigdemont announced Tuesday that he had accepted the mandate for "Catalonia to become an independent state" and signed an independence declaration but asked regional lawmakers to suspend it to allow for dialogue with Madrid. The legal validity of the declaration was unclear.
After holding an emergency cabinet meeting, Rajoy told lawmakers that Puigdemont had until next Monday to decide if he planned to push ahead with secession and until next Thursday to reconsider, otherwise Madrid would suspend Catalonia's regional autonomy.
The deadline set the clock ticking on Spain's most serious political emergency since its return to democracy four decades ago.
"We ask for dialogue and the answer by putting article 155 on the table. Understood," Puigdemont tweeted late on Wednesday.
Demanes diàleg i et responen posant el 155 damunt la taula. Entesos.— Carles Puigdemont (@KRLS) October 11, 2017
Spanish foreign minister Alfonso Dastis said in an interview on Tuesday that the government would push ahead with article 155 powers "with prudence and proportionality."