Madrid: Spain’s biggest opposition party is balking at plans to crush Catalonia’s separatists, threatening the coalition Prime Minister Mariano Rajoy assembled to bring the breakaway region to heel, according to two people with knowledge of their discussions.

The Socialists backed Rajoy before he unveiled measures to restore control on Saturday by seizing the administration in Barcelona. The party’s leadership is concerned the conflict will escalate unnecessarily if the Catalans are backed into a corner with no options other than to declare independence, one of the people said. They asked not to be named discussing internal matters.

The tensions add another layer of intrigue to a crunch week for the country’s most dramatic political crisis for almost four decades.

The Catalan leadership is planning to mobilize a human shield to block efforts to implement Rajoy’s declaration to reassert his authority. The problem for Rajoy is that the more force he exerts, the more strain he is placing on the complex network of alliances that underwrite that authority.

The backing of the Socialists and the Cuidadanos party allowed the prime minister to claim he was leading a broad consensus—crucial political cover before taking action that would invite a backlash among many Catalans.

He held a series of meetings with Socialist leader Pedro Sanchez and Albert Rivera of Ciudadanos before deciding to use the wide-ranging—though untested—powers of Article 155 of the Spanish Constitution. The three parties together have 250 of the 350 seats in the national Parliament in Madrid.

Sanchez made it clear to Rajoy in their talks that the Socialists would not support him using Article 155 if the Catalan government retreated from its claim to independence, one of the people said. The plan would be to call regional elections instead.

“In difficult times, we have to measure up and take responsibility," Sanchez said on Twitter before a meeting of the party’s national executive on Monday. “That’s what people demand from us." One former minister, a Catalan, quit the party in protest at its decision to support the use of Article 155.

Pablo Casado, deputy secretary general of Rajoy’s People’s Party, and justice minister Rafael Catala both said Tuesday that even if Catalonia president Carles Puigdemont were to call a snap election, that wouldn’t be enough now to deter the government from using its powers. Bloomberg