On Dec. 20, Spaniards will vote in the country’s general election. Many voters are concerned about Spain’s slow economic recovery and double-digit unemployment, and in Catalonia, the second-most populated region in Spain, secessionist sentiment is very strong.

Many Catalans think of Catalonia as a different nation from Spain, with its own language, culture and traditions, and they have a strong desire for self-government. After a reform to extend Catalonia’s self-government powers was cut short by Spain’s Constitutional Court in 2010, public support for independence has increased substantially. The Catalan pro-independence parties won a victory in the regional election in September. Many Catalans believe that the outcome of next Sunday’s election will have serious consequences for Catalonia’s drive for independence. Here’s why.

The current Spanish government is under challenge

For the past four years, Spain has been ruled by the conservative Popular Party, led by Prime Minister Mariano Rajoy, with an outright majority. The primary opposition party, the Socialist Party, lost power in 2011 and is now trying to get back into office with a center-left program that would end cuts to social spending.

The bipartisan system that has dominated Spanish politics since 1978 will be likely come to an end after Sunday’s election. Two new political parties are expected to gain a substantial number of seats: Citizens, a center-right political party, which raises the flag of democratic regeneration and anti-corruption; and Podemos, or We Can, a left-wing party heir to the anti-austerity movement.

Recent polls suggest that the Popular Party will win the election — but with only a plurality of seats, not an outright majority, forcing the conservatives to find a parliamentary ally. The Socialist Party is also expected to lose seats, although it may still be able to hang on to second place.

But many voters are disgusted with the country’s economic decline and corruption. Younger voters especially are disillusioned with those two traditional leading parties. As a result, the two new parties — Citizens and Podemos — will benefit and will threaten the Socialist Party’s second place.

Podemos is too far to the left to even consider an alliance with the Popular Party. Because the Socialist Party has been the traditional opposition, it probably cannot risk alienating its voters by joining with the Popular Party. The center-right Citizens seems the likeliest option for an alliance with Popular if both parties combined can secure a majority.

How will all this affect the status of Catalonia?

Rajoy, so far, has rejected Catalan nationalist parties’ demands for a referendum on independence. He argues that that would be unconstitutional — but he has failed to propose any reforms to settle Catalans’ grievances, which range from central government interference on linguistic rights to a desire for greater fiscal autonomy. Madrid’s unwillingness to compromise has, unsurprisingly, persuaded more and more Catalans to back independence.

This September, Catalan secessionist parties won an overall majority in the regional parliamentary election, with almost 48 percent of the vote.

That’s not a full majority. Yet Catalan secessionist parties have felt strong enough to push for unilateral measures backed by the pro-independence majority in the regional parliament, which include a declaration to begin the process of independence from Spain, the drafting of a new constitution for Catalonia and the defiance of any further rulings against Catalan self-government by Spain’s Constitutional Court. The pro-independence movement has been peaceful but persistent, suggesting that the next Spanish government will be under pressure to make some concessions.

The Spanish parties have genuine differences about how to deal with Catalonia’s independence aspirations. The leftist newcomer Podemos is open to a referendum on Catalan independence. The center-left Socialist Party propose a federalist constitution that would strengthen the regions’ powers in the Spanish Senate and would recognize, albeit somewhat ambiguously, the “singularities” of Catalonia. The center-right Citizens, also open to constitutional change, wants to strengthen the central government instead. The Popular Party prefers that the constitution be left as it is.

But given the increasing Catalan pressure and the Popular Party’s probable loss of power, the next Spanish government will have to launch some reform process. In Catalonia, the most popular move would be for the new government in Madrid to grant Barcelona further political, cultural and fiscal autonomy, including complete autonomy on language issues and the education system and greater control over this wealthy region’s tax revenue.

Many Catalans also want their region recognized as part of a plurinational Spain that is seen as a voluntary union of diverse peoples with different languages and traditions. The recognition of the distinctiveness of Catalonia with its own language and specific history of self-government would better correspond to the view of many Catalans. Many in the region reject the notion of Spain as a homogeneous, Castilian-Spanish-dominated nation. They resent the fact that Catalonia is treated as just another region.

This is unlikely to happen because only Podemos shares this idea of Spain as a “nation of nations.” The other three main parties insist on Spain as a unitary, homogeneous nation and on equality among all Spaniards, which effectively means that there is only one — or good — way to be a Spaniard: that of the majority.

In Catalonia, Podemos may win the most parliamentary seats. That’s because Podemos, of all four major parties, is closest to backing secessionist demands. In past elections, no major Spanish national party would have considered supporting a Catalan independence referendum. What makes the move by Podemos even more surprising is that other political parties — especially the Popular Party — have criticized “concessions” to Catalonia to win votes elsewhere in Spain.

In fact, Podemos wants to appease Catalan secessionist demands by reforming the constitution to transform Spain into a federation with semi-independent nations, declaring that the country is the product of a voluntary union of diverse peoples. This would allow Catalonia to decide its relationship with the rest of Spain in a referendum. The Socialist Party, which strongly opposes Catalan nationalism, will support opening up a constitutional debate but rejects an independence referendum.

In the previous election in 2011, the Popular Party ranked third in Catalonia. This time, it is expected to slide to sixth place, behind two nationalist parties, the Socialist Party, Podemos and Ciudadanos.

For parties that seek to hold back a Catalan secession, opening the process of constitutional reform may be smart and necessary for several reasons. Doing so would halt Catalan nationalists’ unilateral attempts to secede, because Madrid will finally have declared itself open to dialogue. Even if nothing comes of the discussion, Madrid will have demonstrated to Catalans that it is willing to take action and that discussing a constitutional reform will gain time for the Spanish parties.

Catalan nationalists are quite divided among themselves. The two parties that constitute a pro-independence majority haven’t been able to agree to form a government — in large part because they have serious differences on socioeconomic issues.

Launching constitutional reform would probably put pressure on Catalan secessionists’ unity, with tensions between the radical and moderate factions likely to arise on whether to engage in a reform process. But simple delay through constitutional discussion will not hold back the Catalan pro-independence parliamentary majority for long.

Because all Spanish political parties reject Catalonia’s independence, Catalan secessionist hopes are likely to be dashed in this election — but if no significant reforms are made, by 2019 an outright majority of Catalonia is likely to back full independence.

David Martí is a D.C.-based political scientist who recently received his PhD from the University of Edinburgh. Martí tweets at @davidmarti70.