Its report, which the union said is the first major study into LGBT sexual harassment at work in the UK, found that more than two in five (42%) LGBT people had unwelcome comments or questions about their sex life from colleagues.
More than a quarter (27%) reported receiving unwelcome verbal sexual advances.
Yet, of the 68% who had experienced sexual harassment, two-thirds (66%) said they did not tell their employer about it, with 25% saying they didn’t report it for fear of being ‘outed’ at work.
The research also found that LGBT women were more likely to experience unwanted touching and sexual assault at work than LGBT men.
More than a third of LGBT women (35%) reported they had experienced unwanted touching, for example placing hands on their lower back or knee, around a fifth (21%) reported experiencing sexual assault, and one in eight (12%) said they had been seriously sexually assaulted or raped at work.
The figures were even higher for BAME women and disabled men and women. More than half (54%) of LGBT BAME women said they had experienced unwanted touching, 45% reported sexual assault and more than a quarter (27%) reported serious sexual assault or rape.
Meanwhile half (50%) of LGBT disabled women reported unwanted touching, nearly four in 10 (38%) reported sexual assault and almost a quarter (24%) reported serious sexual assault or rape. LGBT disabled men also reported higher levels of sexual harassment and assault than non-disabled LGBT men, with more than one in four (28%) disabled men reporting sexual assault.
LGBT people told the TUC these experiences had severely affected their lives. Around one in six (16%) said sexual harassment at work affected their mental health. The same proportion (16%) said they had left their job as a result of being sexually harassed, while one in 25 (4%) described the experience as so unbearable that it caused them to leave their job without another job to go to.
TUC general secretary Frances O’Grady said the research reveals a "hidden epidemic" in UK workplaces: "In 2019 LGBT people should be safe and supported at work. But instead they’re experiencing shockingly high levels of sexual harassment and assault.”
O’Grady added that employers and the government must work together to tackle the problem.
“Workplace culture needs to change. No-one should think that a colleague being LGBT is an invitation for sexualised comments or inappropriate questions – let alone serious acts of assault," she said.
“The government must change the law to put the responsibility for preventing harassment on employers not victims. And anyone worried about sexual harassment at work should join a union.”
Laura Russell, director of campaigns, policy and research at Stonewall, said: "These are shocking figures into what some lesbian, gay, bi and trans people experience in the workplace. All employers have a legal duty under the Equality Act 2010 to ensure LGBT people are free from discrimination. But we know from our own research and this report that LGBT people still face abuse and discrimination in Britain’s workplaces. Stonewall works with employers through our Diversity Champions programme to develop zero-tolerance policies on anti-LGBT discrimination and encourages businesses to communicate clear routes to report bullying and harassment at work."
The research highlights an increased need for better education added Harry Small, equity partner IT/commercial practice at Baker McKenzie: “This shows the importance of education of employees about their lesbian, gay, bisexual and trans colleagues from the first day of work. This education above all should help people to understand the hurt that can be caused to LGBT people if their orientation and relationships are not accepted and recognised to be as important and valid as straight people and their relationships," he said.
Paul Holcroft, associate director of operations at Croner, added that employers need to review their D&I policies.
"One of the key actions an employer can take is the production of a new diversity and inclusion policy. The policy could outline what the company intends to do to challenge outdated stereotypes and promote equal opportunities for LGBT and other minority workers," he said.
"This could be done through the setting of specific targets. For example, the BBC’s Diversity and Inclusion Strategy aims to have 8% of its workforce be from the LGBT community by 2020 through changes to its recruitment and selection processes. By taking this action a company can help to encourage its current workers not to feel segregated in their roles while also promoting itself to potential external candidates. A visible policy could also enable the organisation to take part in local networking or ‘pride’ events, which would help to facilitate further exposure to the community."
The research was conducted to coincide with the international inernational Day Against Homophobia, Transphobia and Biphobia today.