MADRID (Reuters) - Spanish Prime Minister Mariano Rajoy is struggling to secure support from across the traditional political divide in his battle to stop Catalonia breaking away - a lack of consensus that could compound Spain s worst political crisis for decades. Rajoy is mulling the unprecedented step of invoking the constitution to dissolve the Catalan parliament and trigger regional elections, ruling party lawmakers say, after Catalonia held an independence vote on Sunday despite violent attempts to stop it. Sacking the Catalan government is known in Madrid as the  nuclear option , given it is considered likely to foment unrest in Barcelona and through the rest of the heavily industrialized, affluent region that accounts for a fifth of Spain s economy. However, Rajoy s People s Party (PP) governs in minority and before playing this trump card, it has been in talks with the main opposition party, the Socialists, to seek their explicit support for such a move, a leading PP lawmaker said. Article 155 of the 1978 constitution has never been used in a country where fascist dictatorship is a living memory. The conservative PP is seen by Catalans as historically connected to the era of late dictator Francisco Franco, so experts say Rajoy must have the Socialists, also strong unionists, on board.  The 155 needs wide-ranging backing because we don t know whether it will resolve problems, and if it s only backed by one party in congress then it will be difficult to obtain the backing of a majority of Catalans,  said Rafael Hernando, who serves as a parliamentary organizer for the PP. Without that backing, Rajoy s hand could be weakened and, according to political sources and analysts, he might ultimately call a snap national election to win a mandate to take on the Catalan separatists. The prime minister s office declined to comment. Participants in the referendum opted overwhelmingly for independence, but turnout was only about 43 percent given that Catalans who favor remaining part of Spain mainly boycotted the ballot. The Socialists, who had been open to the Article 155 option before the referendum, appeared to shift position this week after police used batons and rubber bullets to stop Catalans from voting - scenes that drew international condemnation. Instead, they said this week they would move a parliamentary motion criticizing Rajoy s deputy, Soraya Saenz de Santamaria, who they blame for the police violence on Sunday. The motion, a symbolic reprimand, does not oblige a minister to step down. There are some influential members of the party, such as former Socialist deputy prime minister Alfonso Guerra, who want Rajoy to take a hard line on Catalan separatism.  The Socialists should vote in favor (of Article 155),  Guerra said on Tuesday. His party, he added, should reprimand Catalan leader Carles Puigdemont, not Saenz de Santamaria. Invoking Article 155 only needs approval of Spain s senate, which the PP controls, but majority political support for such a bold step in the lower house would help protect Rajoy against any no-confidence motions from his other political opponents. The left-wing Podemos party opposes using the article and wants Rajoy to negotiate a new referendum on independence, this time with his blessing. Madrid had banned last Sunday s referendum as unconstitutional, deploying police to disrupt it in what even some of his allies regard as a political mistake. The Basque National Party, formed to campaign for greater autonomy for the northern Basque region, is also against sacking the Catalan government. Last week, it withdrew support for Rajoy s 2018 budget until the Catalan question is resolved. Antonio Barroso, deputy director of London-based research firm Teneo Intelligence, said the Socialists  position on using Article 155 could be critical to Rajoy s future.  Basically he is taking the country into uncharted waters and for that he wants maximum support from as many parties as he can get on board, but also for wider acceptance of the course of action that the government will pursue,  Barroso said. Rajoy has offered to open multi-party talks that could cut a better tax and constitutional deal for Catalonia in return for the region giving up on independence. But Sunday s violence has hardened many Catalans against any such compromise. So far, only center-right Ciudadanos said this week it was in favor of sacking the Catalan government, dissolving the parliament and holding regional elections. Reflecting his struggle to find broader support, Rajoy has postponed until at least next week an expected parliamentary debate on Catalonia. By then, though, it might be too late. A member of Catalonia s pro-independence Popular Unity Candidacy party, a member of the region s governing coalition, said on Wednesday Catalonia would move in the regional parliament on Monday to declare independence. 