More than 170 staff quit the immigration department during the first three months of 2006, it has emerged.
The government has set targets for faster immigration claims
Nearly one out of every five returned a questionnaire saying it was because of discrimination, harassment or bullying.
One ex-employee said she was bullied by managers trying to meet targets to deal quickly with immigration claims.
A Home Office spokesman said: "Our policy on bullying is very clear. It is unacceptable, as is any other form of harassment, and will not be tolerated."
The spokesman added: "We strongly encourage people to report wrong-doing if they suspect it is taking place.
"It is obviously in the public interest that any wrong-doing should be exposed."
Official figures released to Channel 4 News under Freedom of Information legislation showed 171 people resigned from the Immigration and Nationality Directorate (IND) in the first quarter of 2006.
Of these 32 returned a questionnaire saying discrimination, harassment or bullying had made them quit.
IND director general Lin Homer told Channel 4 News: "We would always take any allegation of bullying very seriously. We simply will not tolerate it.
The department was trying to "get much more involved with our staff, in getting them to talk about issues, to report them when they occur and being very clear that if they do we will take action", he added.
But one ex-worker, who did not wish to be named, told the programme workers checking applications to stay in Britain had been under constant pressure to approve them quickly rather than seek extra information, which might have resulted in them being rejected.
"You were not given any credit for using your brains and finding out that something was falsified," she added.
"You were meant to skim over the top. If it virtually looked all right and it met most of the criteria, then you were to grant it.
"If you carried on, and you dug, or you thought something was a bit off, you were penalised for it.
"You lose out on your money, not meeting your targets, and being told that you have got to perform better.
"We actually ended up with the management team stopping you from refusing, and saying that you are being too picky, and you should have just granted that person."