Eight illegal immigrants were arrested after UK Border Agency officers inspected a Warburtons bakery in Enfield last month.
With Warburtons' cooperation, officers checked whether employees had the right to work in the UK. Eight illegal immigrants were uncovered six from Pakistan, one from Zimbabwe and one from South Africa.
"We believe we have robust processes in place and are fully compliant with relevant legislation," said a spokesman for Warburtons. "We have given, and will continue to give, the UK Border Agency our full support until this matter is resolved."
The Agency has warned that fraudulent identification is becoming more difficult to spot.
A spate of raids recently uncovered a number of illegal workers in food and drink firms, including Fresh'n'Fast Quality sandwich factory on the Abenglen Industrial Estate in Hayes, and Buckingham Foods' sandwich factory in Milton Keynes.
UK Border Agency London area director, Sharon Flannery, said: "We are happy to work with businesses to ensure the right checks are done on staff. But those who are found to have broken the law will face action."
Fines of up to £10,000 for each illegal employee can apply.