UK immigration officials have discovered a total of 13 people working without the correct UK work permits or immigration documents.
The offenders were discovered at four different businesses after UK Border Agency (UKBA) officers conducted raids in Cardiff, Rhyl, and the Amman and Swansea valleys on the back of intelligence.
In total the raids uncovered two men from Pakistan, six from Bangladesh, one from Malaysia and four from China - all working in a number of different businesses in Wales.
The offenders were arrested and arrangements are being made to deport the majority of them for not having the correct UK visas or UK work permits.
Meanwhile, the businesses involved could face significant fines if they are found not to have carried out the correct right-to-work checks on their employees.
Firms can be fined up to £10,000 per illegal employee if they are discovered to have not asked for a UK work permit or a passport before employing the individual.
All four of the businesses concerned have already been issued with a penalty notice for employing illegal workers.
Jane Farleigh, regional director of the UKBA in Wales, commented: "Illegal working undercuts businesses that stay within the law and exploits foreign workers.
"As long as there are opportunities for illegal jobs the UK will be an attractive place for illegal migrants - that is why we are putting a stop to employers who do not play by the rules."