Cue accusations of hypocrisy and a debate about loyalty to friends over political principles -- all of this occurring with national elections 12 weeks away.
The wedding is in Vitoria, in the Basque country, between Rajoy political ally Javier Maroto and his partner Josema Rodriguez. Maroto is a senior official of the governing Popular Party, or PP, which Rajoy leads. Not only has Rajoy said he plans to attend; a PP colleague has disclosed he's an official witness of the marriage.
'Will he, won't he go?' has taken up acres of Spanish media coverage and spawned a new hashtag on Twitter: #laBodaDeMaroto (the marriage of Maroto). While it's unlikely to dominate the election campaign, the event has led to dissent between the conservative and more centrist factions of Rajoy's party. It may also be politically awkward since the party's base is among the older and (by and large) more conservative Spaniards.
El Mundo, one of Spain's leading dailies, said Interior Minister Jorge Fernández Diaz has warned Rajoy that attending Maroto's nuptials would contradict the Popular Party's record. Diaz said pointedly he did not receive an invitation. But other party figures did. Andrea Levy -- a rising star -- said she is going and plans to enjoy the occasion.
The opposition Socialist Party is enjoying the Prime Minister's discomfort, congratulating Maroto on his wedding and expressing pride that the law it passed a decade ago should have brought happiness to so many people. Twisting the knife, party spokesman Angeles Alvarez tweeted that Rajoy is planning to celebrate in private what he persecutes in public.
Senior figures in the Popular Party have tried to play down the issue. Esperanza Aguirre, who leads the PP on the Madrid City Council, said the party is not a sect and there's room for differing views. As for Maroto, he said he'll understand if the Prime Minister does not attend because 'he's busy with the regional elections in Catalonia.'
In an effort to limit the political fallout, Maroto said that while his party does oppose same-sex marriage, it supports the rights and obligations of such unions and it hasn't tried to reverse the law in the current parliament. He said his relationship with the Prime Minister will not be affected whether the leader attends or not, and he doesn't want 'a private event to become a media circus.'
Same-sex marriage called 'poke in the eye' to Catholics
In 2005, Spain became at that time the third country in Europe to recognize same-sex marriage. Rajoy protested in parliament on the day the Socialists, then in the majority, passed the law.
Since then, he has continued to insist that marriage must be between a man and a woman -- and that same-sex couples should be content with civil unions. As leader of the opposition, Rajoy and others in the Popular Party challenged the law in Spain's Constitutional Court, saying that it 'perverts the basic institution of marriage.' Rajoy also said that allowing same-sex marriage (as opposed to civil unions) was a 'poke in the eye' to Catholics.
In an 8-3 vote, the court eventually rejected the appeal. In a ruling in 2012, the court recognized that in same-sex marriage 'a step forward is being made towards guaranteed personal dignity and the free development of one's personality.'
'In Spain there is broad social acceptance of marriage between same-sex couples,' the court added -- citing opinion polls that support same-sex marriage.
But before the last election, many same-sex couples in Spain feared that Rajoy would try to reverse the law if his Popular Party won. Some hastened to tie the knot, which made the village of Campillo de Ranas north of Madrid -- (population 184 in the last census) -- a busy place. Its mayor had come up with a novel way of battling Spain's crippling recession: welcoming same-sex couples to wed.
The importance of social issues to Rajoy's supporters
Maroto's wedding has briefly diverted attention from the other main issues of Spain's upcoming election: the economy and Europe's refugee crisis.
Rajoy -- who has taken a hard line on migration -- eventually agreed to the European Commission's request that Spain take some 17,000 of the current tide of refugees entering Europe. Some cities led by left-wing parties have taken the initiative on providing shelter and support to refugees.
The Prime Minister has focused on economic recovery as the main achievement of the Popular Party's five years in power. Spanish banks have been rescued, unemployment has fallen and Spain enjoys (at 3.1%) one of the highest rates of growth in the European Union. Some 500,000 jobs were created in 2014, although youth unemployment remains stubbornly high.
But social issues remain important to a significant faction of Popular Party supporters and politicians. After abandoning a proposal to ban abortion on demand, the government recently pushed through a measure forbidding minors from having an abortion without parental consent. Even so, several of the party's senators voted against the measure as inadequate.
Opinion polls suggest no party will gain an overall majority in December's elections, as two new groups -- Ciudadanos and Podemos -- threaten to take votes from the Popular Party and Socialists, respectively. Podemos is an insurgent left-wing party similar to Syriza in Greece; Ciudadanos is a centrist pro-business party.
There is also the wild card of Catalonia, where parties promising a path to independence and those content with autonomy do battle in regional elections at the end of September. If the pro-independence parties secure a majority of votes, they plan an 18-month transition to secession from Spain.
Antonio Roldan Mones of risk consultancy Eurasia Group expects that in the national elections at least three parties will be needed to form a viable coalition, with the Popular Party likely to emerge the largest on the strength of its economic record. It may also benefit -- after the Catalan elections -- from being seen as the best guarantor of Spain's unity.
But in any event, he expects forming a new government 'will be very difficult' and a new constitutional amendment may be needed to decentralize power further -- in education, language rights and finance -- to meet Catalan demands.
In Vitoria, Maroto may just be looking forward to Saturday and married life. He told the Spanish radio station COPE he hopes that one day weddings such as his will not be big news -- and that everyone will accept them as normal.