Danish company Vestas Windsystems plans to make 625 workers redundant at the end of July, despite rising profits.
Workers said the fence was being built to stop food or drink being sent in, which has led to complaints that the company is acting illegally.
Vestas said talks at the site were continuing and it would not comment.
Protesters, who occupied the Newport site on Monday at about 1930 BST, said managers had given them until Tuesday night to end their action or face the sack.
BBC South Today reporter Tom Hepworth has learned the 24 protesters have been sacked and the electricity and telephone lines in the building have been cut.
'Denied aid'
"It's appalling," said one of the workers.
"We are convinced this is against the Human Rights Act because we are being denied humanitarian aid.
"But the more the management try to flush us out, the more determined we are to dig in our heels."
A total of three people have now been arrested at the site, police said.
A man was being held on suspicion of assaulting an officer, and another for breach of peace.
The men, who are from Southampton, are aged 28 and 49.
Earlier, a 38-year-old London man was arrested on suspicion of breach of the peace on Wednesday after he tried to enter the site.
He was released without charge.
RMT union leader Bob Crow said: "I think it is absolutely scandalous what is going on and we are supporting this occupation.
"These people are being denied food, they are being denied water."
The campaigners have called on Ed Miliband, the energy and climate change secretary, to travel to the island to speak to them.
About 200 workers staged a protest outside the factory on Tuesday after being turned away when they arrived for work.
They were also joined by climate change protesters who are supporting them.
Police said Vestas had started legal action to gain an injunction which would remove the sit-in protesters.
The company said the factory was being closed next week due to reduced demand for wind turbines in northern Europe.
Friends of the Earth's energy campaigner Nick Rau said: "The UK has the best wind resources in the whole of Europe and we should be creating green energy jobs, not shedding them.
"Why hasn't the government supported Vestas as it has the car industry, and taken enough action to keep wind turbine manufacturing jobs here in the UK?"
A spokeswoman for the Department of Energy and Climate Change said the plant made blades for the US market which were not the right specification for onshore or offshore wind farms in the UK.
"We are hopeful that Vestas will go ahead with their plans for a research and development facility on the Isle of Wight which could provide up to a further 300 jobs and also help develop and test products that are suitable for the UK offshore market."
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