New sexual harassment legislation, aimed at tackling discrimination in the workplace, has come into force.
The law has been amended to help tackle harassment
The European Equal Treatment Directive has extended the definition of sex discrimination to cover any act that leads to intimidation or degradation.
The TUC said the changes would make employers more responsible and allow female workers a better chance of fighting against harassment.
But businesses said the law would see companies facing "legalised blackmail".
Under the new law, a colleague who persists in making remarks about a woman's appearance could be accused of sexual harassment.
Sarah Veale of the TUC told BBC Five Live employers had a duty to protect their staff.
"The employer is vicariously liable. Often the employer will sit back and let it go on.
"An employer should make sure that the people it employs know how to behave and if they're causing offence to others then they should do something about it," she said.
In a separate statement, TUC general secretary Brendan Barber added: "Today's 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 Rex Garratt, spokesman for the Forum of Private Business, which represents more than 25,000 small to medium sized firms, said the changes were too heavily in favour of employees.
"Employers will view these changes to tribunals with a sense of utter dread.
"Tribunals are already bleeding businesses dry because they are so heavily loaded in favour of employees.
"Businesses face legalised blackmail as the costs of defending a case deny them justice from vexatious ex-employees on the make, supported by ambulance-chasing advisers who encourage doubtful claims."
He added private businesses had become a "prime target for the compensation culture".
"This compensation culture has seen a doubling in the amount of compensation awarded in 2004 in the key areas of sex, disability and racial discrimination."
A spokeswoman for the Department of Trade and Industry said the Employment Equality (Sex Discrimination) Regulations 2005 amend the law to "make explicit the fact that discrimination on the grounds of pregnancy and maternity leave and sexual harassment and harassment on the grounds of sex are unlawful.
"We also took the opportunity to amend the Sex Discrimination Act, so that it is in line, as far as possible, with other legislation tackling discrimination on the grounds of race, disability, religion or belief and sexual orientation in the fields of employment and vocational training," she said.