New sexual harassment legislation, aimed at tackling discrimination in the workplace, came into force over the weekend.
The European Equal Treatment Directive has extended the definition of sex discrimination to cover any act that leads to intimidation or degradation.
Under the new law, an employee who persists in making remarks about a woman's appearance could be accused of sexual harassment.
TUC general secretary, Brendan Barber, said: "The change will force employers to take their responsibilities towards providing a harassment-free working environment more seriously.
"There's no place in the modern workplace for office gropers and lechers and bosses need to do more to stop those responsible for bad behaviour from making working life unbearable for thousands of women."
But employers’ groups said the law would see companies facing "legalised blackmail".