A Spanish pro-life group said it plans to protest the arrival on Thursday of a Dutch boat that is offering to provide abortions that circumvent Spain's strict laws.
The boat is due to anchor off the Mediterranean port of Valencia, the Dutch non-profit organisation Women on Waves said on its web site.
From Friday, it will offer abortions on the ship in international waters under the Netherlands' more liberal abortion laws.
This "symbolic initiative" will allow "abortions outside Spanish law for the first time in Spain's recent history, but without violating it," said Spanish gynaecologist Josep Lluis Carbonell, one of the promoters.
But it has already sparked controversy.
Valencia's conservative mayor Rita Barbera termed the plan a "provocation that has sparked indignation."
The anti-abortion group Provida in Valencia said its members plan a protest aboard a smaller vessels when the boat arrives.
Spain decriminalised abortion in 1985 but only for certain cases: up to 12 weeks of pregnancy after a rape; up to 22 weeks in the case of malformation of the foetus; and at any point if the pregnancy represents a threat to the physical or mental health of the woman.
But the Socialist government last month said it plans to introduce a new law that will offer greater legal protection for women who wish to have an abortion and doctors who carry out the procedure.
The Women on Waves ship visited Ireland in 2001, Poland in 2003 and Portugal in 2004, sparking protests in each country.