The investigation comes as the Government launches a support service to protect young people's right to fair pay.
HMRC, which is responsible for enforcing the minimum wage, will send out letters to 200 employers who recently advertised intern opportunities and follow this up with targeted checks. Last year, HMRC identified 736 employers who paid staff less than they were entitled to or nothing at all.
"Leaving education and getting a job for the first time can be daunting for any young person," said employment relations minister Jo Swinson.
"Internships can provide an important first step and are often a valuable way of helping young people start work. They should be open to everyone in a fair and transparent way."
Charity exploitation
Trade union Unite today urged HMRC to investigate charities it claims are exploiting unpaid interns.
Unite, which has 60,000 members in the not-for-profit sector, has given evidence to the Low Pay Commission that more than a third of the UK's top 50 charity employers are signing up unpaid interns.
Unite said it will be writing to HMRC to urge action against "this exploitative and elitist practice, which trades on the goodwill and compassionate nature of young people."
Unite national officer for the not-for-profit sector Sally Kosky said: "The HMRC is charged with enforcing the national minimum wage and we would urge them to take action where it is clear that young people doing an unpaid intern role are actually doing a proper job of work and should be paid accordingly."
Last week, the Government's social mobility tsar Alan Milburn called on employers to axe unpaid internships in order to ensure fair access to Britain's top jobs.
The Labour MP, whose role is to advise Government on social mobility issues, argued that growth in professional employment is not creating a new "social mobility dividend" for the UK.
