Prime Minister Mariano Rajoy's Popular Party promised, in a manifesto ahead of its 2011 election victory, "to reinforce protection of the right to life".
That was a nod to opponents of a landmark 2010 reform by the former Socialist government, which brought Spain into line with much of Europe by letting women freely opt for abortion in the first 14 weeks of pregnancy.
But nearly 18 months after the Popular Party took power, the justice ministry, which is in charge of the reform, has still not drawn up any concrete proposals amid signs of internal dissent.
"There is a lot of speculation that it is being slowed down by differences of opinion in the party itself and in the government," said Ferran Requejo, a political scientist at Pompeu Fabra University in Barcelona.
"There is resistance in the party because they can't agree on the criteria for aborting and there is no agreement in the government because of the image it gives of Spain in Europe."
Before 2010, abortion was a crime in Spain except in cases of rape, risk to the mother's health or deformation of the foetus.
Justice Minister Alberto Gallardon has indicated in press interviews and in parliament that he wants to return to a law similar to that one, but also to go further, curbing abortions in cases of deformation.
A study by pollster Metroscopia published last month in centre-left newspaper El Pais indicated that 46 percent of Spaniards favoured keeping the law in its current form while 41 percent wanted a stricter system such as that planned by Gallardon.
Last month, the head of the Roman Catholic Church in Spain, Cardinal Antonio Maria Rouco Varela, called for an "urgent reform" of the 2010 law, which he said had "led to a rise in the number of abortions to terrifying levels".
Within hours, Gallardon announced that the government would pass the reform "promptly", sparking speculation that he was under pressure from the Church, considered a powerful lobby in the party.
"Gallardon at one time was the leader of the most liberal section of the party. He has made a U-turn since he has been in the government, and has become the leader of the most hardline section, those closest to the Catholic Church when it comes to abortion," said Requejo.
"Some people speculate that he is going to put himself forward as an alternative to Rajoy in the next election, when the most right-wing section of the PP wants to replace Rajoy."
The justice ministry and the Popular Party told AFP they would not comment on the reform since it was still being discussed.
Rajoy as well as Health Minister Ana Mato and other members of the government have avoided commenting on details of the reform.
Mato has defended Gallardon in parliament, however, and said the future law would have the backing of the whole government.
The spokeswoman for the Spanish anti-abortion campaign group Right to Life, Gador Joya, said Gallardon "must know that Spanish society is backing him to carry out this reform".
"What we want is for no woman in Spain to have to go through this ordeal," Joya said in a statement.
Spain's Constitutional Court has yet to rule on an appeal brought against the law by the Popular Party.
"We cannot make the right to life subject to the decisions of one political party or another," Joya said. "The right to life must be protected by the constitution."
On the other side, a platform of pro-choice women's rights groups has launched a joint campaign to keep the abortion law as it is.
"I am convinced that Spanish society no longer agrees that judges, doctors, ministers and lawyers should make women's decisions for them," said the deputy leader of the opposition Socialist party, Elena Valenciano, at the launch of the campaign.
"It is clear there is division" in the Popular Party on the issue, she told AFP afterwards.
"It is also clear there is pressure from the most conservative sections of the party. There must be tension in the government but we still don't know where everyone stands."