The level of sexual harassment in the workplace is "shameful", with women being subjected to unwelcome jokes, verbal advances, suggestive remarks and even demands for sexual favours, says a report.
The TUC said its study showed that the problem was worse for younger women, with almost two-thirds of 18 to 24-year-olds saying they have suffered sexual harassment at work.
A survey of 1,500 women found that a third had been subjected to unwelcome jokes, while one in four received sex-related comments about their body or clothes.
One in four had been touched and one in eight said someone had tried to kiss them.
The TUC said sexual harassment at work took many forms, from suggestive remarks, jokes about a colleague's sex life and circulating pornography, to inappropriate touching, hugging or kissing, or demands for sexual favours.
In most cases, the perpetrator was male, with nearly one in five women saying it was their line manager, or someone with direct authority over them.
Four out of five women who said they experienced sexual harassment at work did not tell their employer, fearing it would affect their relationships at work, hit their career prospects or they were too embarrassed to talk about it.
TUC general secretary Frances O'Grady said: "How many times do we still hear that sexual harassment in the workplace is just a bit of 'banter'?
"Sexual harassment is undermining, humiliating and can have a huge effect on mental health. Victims are often left feeling ashamed and frightened. It has no place in a modern workplace, or in wider society.
"Employers must be clear they have a zero tolerance attitude to sexual harassment and treat any complaint seriously. It's a scandal that so few women feel their bosses are dealing with the issue properly."
Laura Bates, founder of the Everyday Sexism Project, which helped with the report, said: "Many people would like to think that workplace sexual harassment is a thing of the past. In reality, it is alive and well, and having a huge impact on tens of thousands of women's lives.
"These findings reveal the shameful extent of the problem and the reality of the touching, unwanted advances and inappropriate comments women find themselves confronted with while simply trying to do their jobs.
"Employers need to take urgent action to tackle the problem."