A 30p rise in the adult minimum wage to £5.35 has come into force, with rises also for workers under 21.
But it is estimated that at least 170,000 people in the UK do not receive the minimum amount for their work.
Revenue and Customs staff have recovered more than £1.3m for underpaid workers since April.
The CBI says the minimum wage had gone up by 27% since 2002 - and wants a "more modest" rise in 2007 to help firms absorb previous increases.
TUC leader Brendan Barber said employers who broke the law should be "named and shamed".
He said they should also "face tougher penalties, including being forced to give back pay with interest to their staff who've been cheated of their wages".
Employment relations minister Jim Fitzpatrick said the government would crack down on employers who mistreated vulnerable workers.
"Millions of working people have directly benefited from the decent minimum standards we have put in place, like the minimum wage.
"This has given employees the security of knowing they can expect fair treatment, wherever they work.
"I want everyone to be aware of the rights they have in the workplace, as a step towards ending unfair treatment and discrimination."
The minimum rate for workers aged between 18 and 21 has increased by 20 pence to £4.45, while 16 to 17-year-olds will now receive £3.30, a rise of thirty pence.