Michael Walker said nurses from other countries were also at risk

"Unfortunately a lot of the nurses coming from the Philippines, many of them highly qualified, think they're coming to work in the NHS," he said.

Mr Walker added: "It's a surprise to them when they find themselves working in private nursing homes carrying out menial tasks for low pay and long hours."

In previous cases nurses have resigned en masse and been whisked away by Unison to prevent the possibility of intimidation.

One of the nurses - who did not want to be identified for fear of repercussions - told BBC News Online she had been a qualified nurse for six years, but had been treated as unskilled labour.

They're afraid of the repercussions of speaking out - not only about what might happen to them but to their families back home too

Allen Reilly Filipino community worker

"Even though we work as nurses we also do household chores and some of my colleagues even do the laundry and clean the kitchen" said the 29-year-old.

Under an agreement between the British and Philippines governments the nurses are supposed to earn the same as a British nurse after an initial training period.

But after nearly 18 months the nurse said she was still earning just �11,000 instead of the standard annual nurses wage of �18,000.

One of her colleagues said that like many others, she was too afraid to challenge the home owners.

She added: "I'm very apprehensive really. We keep trying to talk to them but they just give us confusing reasons.

"So we just keep quiet because we're not sure of what's going on."

'Illegal contracts'

Mr Walker said some nursing homes were not only exploiting nurses but also breaking the law through illegal contracts or bans on union membership.

Allen Reilly has been threatened for helping nurses

Unison was taking legal action against some home owners to recover money owed to nurses and for the imposition of illegal contracts, he added.

Community worker Allan Reilly agreed fear of deportation or intimidation was a big factor in keeping many of Filipinos in unsatisfactory jobs.

Mr Reilly - a retired nurse - works with the Filipino community in south London.

He said he started hearing rumours of poor working conditions about a year ago, after many nurses arrived recruited by in the Philippines to work for British hospitals and homes.

"They're worried for their families back home in the Philippines because we're dealing with a multi-billion pound industry and we don't know who the backers are of some of the agencies in the Philippines," Mr Reilly said.

Because of his work helping to relocate nurses he said he had received several threatening e-mails from the Philippines.

Mr Walker said Unison was also planning action in several more cases.

He said he hoped Unison's actions would eventually deter employers from exploiting Filipino nurses but feared some would simply move to easier targets such as nurses from India or Zimbabwe.