A large Garda contingent is expected to be on duty in north Mayo again today to escort Shell staff and contractors into the Corrib gas terminal site in Bellanaboy.
Gardaí yesterday removed protesters and placed them behind crash-barriers. They also removed vehicles.
Gardaí also confirmed that objectors had been filmed by them.
The Shell to Sea campaign says it will maintain its peaceful protest. It described the security operation initiated early yesterday as akin to "martial law".
Mayo Independent TD Dr Jerry Cowley, who lodged a complaint over a delay in giving him medical access to a protester, said he had been "shocked to see how the State could be used to quash a peaceful demonstration".
Dr Cowley described the events as "an abuse of Garda time and resources".
Up to 170 gardaí were involved yesterday from 3am, when all access roads to Bellanaboy were closed. A hundred members of the community had already started to gather - some of whom spent most of the night at the terminal gates - and at about 4am several of their vehicles were removed.
Shortly before 7am, Supt Joe Gannon asked protesters to move and the group sat down and began saying the Rosary in Irish.
Campaigners said this strategy was designed to focus minds when subjected to "intimidatory tactics".
Gardaí then began lifting the protesters and removing them to an area behind crash-barriers. Several of the five men jailed last year for 94 days over their objections to the pipeline were removed with their spouses.
Shortly before 8am, a convoy of minibuses and four-wheel drive vehicles arrived with up to 70 construction workers employed by Shell, Roadbridge and five contract companies.
There were jeers and shouts as the vehicles drove through the gates.
One of the construction workers, Paddy Ruddy, who works for Roadbridge, said later that he was glad to be back at work.
A young woman who was caught in a crush between two gardaí required medical attention. Dr Cowley, who was on his way to support the campaigners, said he had been informed of this but was stopped at one of several Garda checkpoints. He said he was told that he would have to leave his car and walk with three large medical bags.
Dr Cowley treated the woman at the scene for shortness of breath and shock. She was taken to hospital and was later released.
"This was just a young girl participating in a peaceful way," Dr Cowley said.
He added that Philip McGrath, one of the five men jailed last year, had to be given medical treatment for bruising.
Gardaí would not comment on the incidents.
"Shell is talking about the right of its contractors to go to work, but the right of people in this area to associate peacefully, to travel to their own work and homes, and my rights as a public representative and as a medical doctor were breached here today," Dr Cowley said as he left to travel to yesterday's sitting of the Dáil.
"I think we've entered a new phase of irresponsibility and bullying by the State," he added.
Shell said the company was pleased that it had been able to re-enter the terminal site after more than a year.
Consultation with landowners on a modified pipeline route would begin "shortly". The company would not be paying for the extra Garda presence, the spokesman said. He was also not aware that Dr Cowley had been delayed.
