Israel deployed hundreds of extra police at Ben-Gurion international airport on Sunday to prevent peaceful protesters from highlighting its brutal occupation of Palestine.
Police spokesman Micky Rosenfeld said 27 "activists" from various countries had been stopped and denied entry.
They would be put on return flights, he said, adding that he expected "hundreds more."
When asked why the protesters were considered a threat Mr Rosenfeld answered they were "involved previously in different activities."
Four Israelis were arrested at the airport for unfurling a banner reading: "Welcome to Palestine," the theme of the planned protest, which was to include activities such as planting trees in the West Bank.
Campaign co-ordinator Amira Musalam said that no activists had yet managed to get out of the airport and to their final destinations in Palestine, which included Ramallah, Hebron and Bethlehem.
"The aim of Welcome to Palestine is that when we have guests coming to Palestine they should be able to say we are going to Palestine and not to lie," she said.
The purpose of the event was to highlight how Israel controls access to the occupied territory, Ms Mussalam said, noting that travellers who wish to visit Palestine are often detained and questioned for hours by Israeli border police and soldiers.
The heavy-handed government response to the protesters - which included sending lists of "suspected activists" to airlines and telling them to kick them off Israel-bound flights and even threatening carriers with unspecified sanctions - is likely to reinforce the protesters' point.