Employers have been warned that there are "no excuses" for failing to check a foreign national's UK work permit or passport before employing them.
Lyn Sari, head of the UK Border Agency's (UKBA) local immigration team for Hampshire, reminded businesses in the region that it is their legal responsibility to check that staff have the right to work in the UK.
If employees are found without the correct UK work permit or documentation, the firm can face fines of up to £10,000 for each worker.
Ms Sari's comments come after two illegal workers from Vietnam were found discovered in an Andover nail bar.
UKBA officers found a 16-year-old and a 30-year-old working in the Hollywood Nail Bar and issued a penalty notice on the spot.
The older employee has been arrested and remains in custody until officials can remove him from the country; while the 16-year-old is in the care of Hampshire Social Services as a minor.
The company, meanwhile, could face a fine of up to £20,000 if it is revealed that nobody asked for a passport or UK work permit before employing the pair.
Ms Sari added: "The message is clear for employers - we will not tolerate illegal working. It is a crime that not only undercuts local business but also has a serious impact on communities, taking jobs from those who are genuinely allowed to work.