With job openings scarce for young people, the number of unpaid internships has climbed in recent years, leading federal and state regulators to worry that more employers are illegally using such internships for free labor.

Convinced that many unpaid internships violate minimum wage laws, officials in Oregon, California and other states have begun investigations and fined employers. Last year, M. Patricia Smith, then New York’s labor commissioner, ordered investigations into several firms’ internships. Now, as the federal Labor Department’s top law enforcement official, she and the wage and hour division are stepping up enforcement nationwide.

Many regulators say that violations are widespread, but that it is unusually hard to mount a major enforcement effort because interns are often afraid to file complaints. Many fear they will become known as troublemakers in their chosen field, endangering their chances with a potential future employer.

The Labor Department says it is cracking down on firms that fail to pay interns properly and expanding efforts to educate companies, colleges and students on the law regarding internships.