A group of about 50 people is staging a demonstration outside Belmullet Garda Station in Co Mayo tonight.
It follows the arrest of three fishermen in the latest incident in the Corrib Gas pipeline controversy.
The men were arrested earlier this evening for what gardaí describe as public order offences.
At the time of their arrest the men were skippering trawlers protesting at the arrival of the pipe-laying vessel 'The Solitaire' off Glengad.
Members of the Shell to Sea Campaign Group say they are appalled that the Navy is being used to facilitate the planned laying of the offshore pipeline.
They are demanding the immediate release of the three men.
The two arrested men took their trawlers to a nearby pier under Garda escort and were taken to Bellmullet Garda Station.
The men are part of a group which is continuing to oppose the laying of the pipeline on health and safety and environmental grounds.
Shell Ireland says work on laying the pipeline will begins soon as weather conditions permit.
The 'Solitaire' arrived off the Co Mayo coast earlier this evening. The ship had been based in Killybegs for the past month.
Works are to begin in North Mayo within the next few days.
The 83km pipeline will connect the Corrib gas field with a €300m refinery which is being built at Bellanaboy.
Naval vessel the LE Aisling has been deployed to the area as have a number of garda units.