A group of about 100 protestors this morning prevented construction workers from entering the site of the €200 million Corrib Gas Terminal in Co Mayo.
Work on construction of the onshore refinery has been at a standstill for over a year.
Shell Ireland said it was very disappointed and would now be reviewing the situation with gardaí.
The Shell-to-Sea group, which staged the demonstration, said it is still totally opposed to the terminal on health and safety grounds.
The demonstrators began arriving at the terminal site at Ballanaboy shortly after 5am and mounted a protest in front of the main entrance.
Shortly before 8am Garda Superintendent Joe Gannon addressed the group and told them that, while they were entitled to stage their protest, workers who were due at the site had an equal right to enter it unhindered.
A short time later, when a convoy of about a dozen cars and vans arrived with construction workers, the demonstrators began to recite the rosary and refused to allow them through.
After a brief standoff, the workers withdrew.
A spokesman for the Shell-to-Sea campaign, P J Moran, said it was determined to prevent the terminal being built onshore and wanted Shell to locate it at sea.
He said they would not allow the workers to gain access to the site.
Shell Ireland's spokesman, Christy Loftus, said the company was disappointed with this latest development and it would now be reviewing the situation with the relevant authorities.
Work on the site began in May 2005 and was suspended four months later.
About 350 workers were employed at the time. Shell planned to bring 70 construction workers onto the site today.
