The number of workplace sexual harassment complaints to the Equality Commission for Northern Ireland has risen by almost a third in the last five years.
It was “relatively common” and affected all sorts of employers, the watchdog added.
The commission advised all firms to have a clear policy, properly implemented and made known to all staff.
Dr Michael Wardlow, chief commissioner of the Equality Commission, said: “The commission has seen the number of calls to our discrimination advice team by people who believe they have experienced sexual harassment at work rise by 31% over the last five years.”
In 2012/13, 110 calls were recorded to the commission’s discrimination advice line by people who believed they had experienced sexual harassment at work.
That rose to 144 last year.
Dr Wardlow added: “Our advice is that all employers should have a clear policy, properly implemented and made known to all staff, who need to know what behaviour is acceptable in the workplace and what is not.
“And as soon as a claim of sexual harassment is made employers must investigate thoroughly and sensitively, implementing any appropriate follow-up action.
“We provide advice to employers to help them comply with the law and also of course can advise and help people who believe they’ve experienced sexual harassment at work.
“It is clear from our work and the work of others that sexual harassment is still an issue in Northern Ireland.”
In an unrelated blog post, the commission said sexual harassment happened in fast food outlets, care homes, service stations, phone shops, corner shops, banks and laboratories.
It added: “Sexual harassment at work in Northern Ireland is, unfortunately, relatively common.
Meanwhile, two sexual harassment complaints have been upheld in Northern Ireland departments over the last five years, the civil service revealed.
One in the Department of Finance was raised in 2015/16.
The other involving the Department of Agriculture, Environment and Rural Affairs (Daera) dates from 2013/14.
A total of nine claims of sexual harassment had been made across the Stormont departments over the same period, an FOI response said. A further two complaints are under investigation.
The Northern Ireland Civil Service has a dignity at work policy which advises staff what to do if they feel they have been the victim of unacceptable behaviour or if they have been accused.
The FOI also revealed 166 claims of bullying, with 20 upheld over the last five years.
A further 11 are under investigation.
Cara Cash, chief executive of the Nexus NI sex abuse counselling organisation for victims, said there was under-reporting of sexual violent crime in general in Northern Ireland and beyond.
“We are seeing more conversations about sexual violence than we ever have before, and that is a good thing, but there is much more that still needs to be done and we are committed to working with any/all agencies necessary to make sure that the voice of the victim is heard.”