MADRID — The pressures facing the government of Prime Minister Mariano Rajoy mounted on several fronts on Tuesday, as thousands of demonstrators besieged Parliament and Spain’s two largest regions took steps that underscored their deepening economic troubles and displeasure with his austerity plans.

Presenting the biggest domestic political challenge, the leader of Catalonia, Spain’s most powerful economic region, called an early election for Nov. 25 that could turn into an unofficial referendum on whether to split from the rest of the country.

Catalonia’s demands for more autonomy have been fueled by its own financial problems, which forced the Catalan government last month to request $6.5 billion from an emergency fund of $23.3 billion set up by Mr. Rajoy’s government to help regions meet their debt financing obligations.