A Dutch campaign group says its ship offering women medical abortions has been prevented by authorities from entering the Moroccan port of Smir.
The group, Women on Waves, provides abortions and advice from boats anchored in international waters near countries where abortion is illegal.
The group's leader, Rebecca Gomperts, told the BBC it planned to launch "a surprise" in response.
She said the entire harbour was blocked and no-one was being allowed to enter.
Women on Waves has said it was invited to Morocco by a youth group called Alternative Movement for Individual Freedoms.
But the country's health ministry said on Wednesday that the ship would not be allowed to operate in the country and called on the authorities to apply the law against the group and the ship, the AFP news agency reported.
Speaking from an inland location close to Smir, Ms Gomperts declined to give any details about what the surprise action would entail.
She travelled into Morocco separately by air on Wednesday, ahead of the boat.
The boat started its journey from the Netherlands on Monday and was scheduled to dock at Smir on Thursday.
In an earlier press release the group said the ship was able to provide legal medical abortions for women who are up to six-and-a-half weeks pregnant, while it was anchored in international waters.
The group's main intention was to promote the fact that an abortion-inducement drug is actually available to women in Morocco, but most of them were unaware of it, the group said.
Women on Waves said it has also launched a hotline number for women to obtain information about contraception and abortion.
Ms Gomperts said it was not yet clear how many calls had been received as the group was in the process of finding out.
Over the past 11 years, a Women on Waves ship has visited Ireland, Poland, Portugal and Spain, sparking protests from anti-abortion groups.
Morocco was the first Muslim country the group planned to visit.
In cases of illegal abortions performed domestically, women expose themselves to grave health risks by resorting to dangerous methods, Women on Waves says.
The group says that, according to figures published by the Moroccan government, between 600 and 800 abortions take place every day in the North African kingdom.