Canada's Globe and Mail newspaper reported this week that the teachers had been detained, deported or were being investigated, as the Korean authorities continued to rout out the country's illegal workers.

Immigration officers are believed to have raided schools, arresting teachers and recruiters.

The Canadian Foreign Affairs Department reportedly told that paper that in the last two weeks it had logged 50 cases involving English teachers. Of these, 35 teachers have now been deported, five are awaiting deportation and the rest are still under investigation.

However, teachers who spoke to the paper said the number of arrests was closer to 150.

One teacher, who declined to be named, but who is working illegally in Korea, told the paper: "They say what we're doing is criminal, but it doesn't feel that way."

She added: "The whole situation is totally inhumane. I've heard of 70 [foreign teachers] being put in a room with capacity for only 30 or 40. It's not like they were dealing drugs or running guns."

These latest arrests follow the high-profile case in March of two Canadian teachers who were involved in an alleged assault outside a Seoul bar. One of the teachers was found to be working in Korea on a tourist visa. The pair were eventually deported, but not without having to pay thousands of dollars in "blood money"- a form of compensation - to their alleged victim.

Those arrests fuelled a growing resentment towards foreign teachers among locals, due in part to salacious postings on a website for English teachers and a documentary broadcast on Korean television that depicted foreigners as lazy and unqualified.

The Korean government has been accused of launching a campaign against teachers. However, in July, the Korean justice ministry told the Guardian that English teachers were not being specifically targeted in its efforts to remove illegal workers.

Talkthread postings on the English language website EFL-law.org, a site for teachers working in Asia, said some Korean recruiters were luring foreign teachers to the country with the promise of a job and offering them copies of fake degrees to get them through immigration.

Some English teachers working legally have, however, welcomed the crackdown, saying illegal workers are harming the profession.

Officials put the number of English teachers working legally in South Korea at 7,800. The number of those working without the necessary documentation is believed to be around 20,000.

An increase in the number or private schools - or hagwons - is blamed in part for the rise in illegal workers. These schools often flout labour and immigration laws and employ unqualified teachers.