Black councillors at women's day event asked 'are you cleaners?'
Three black councillors attending an International Women's Day conference in London were asked by staff if they were there to clean, it has emerged.
Hackney Borough councillors Sophie Conway, Carole Williams and Sade Etti attended the City Hall event and said they were challenged by security.
"We were quite stunned at the time," Ms Conway said.
Greater London Authority said it did not tolerate discrimination and was investigating the matter.
A spokesman said the Greater London Authority took complaints of this nature extremely seriously and would take action if it was found to be appropriate.
The event was held on 10 March, two days after International Women's Day, which celebrates how far women have come in society and aims to raise awareness of sources of inequality.
It was organised partly as a networking event and was attended by businesswomen, campaigners, charity workers and women from a range of backgrounds.
Ms Conway, Labour councillor for Hackney Central, said: "When we arrived at City Hall we were met by two security guards who asked us what we were there for.
"When we explained what event we were there to attend, we were asked if we were there to clean it. We were quite stunned at the time so we sort of stood there in disbelief."
Ms Williams, Labour councillor for Hoxton West, who is also a part-time doctoral researcher, said: "There was an instant recognition on his face as soon as the words came out of his mouth, so he knew what he had said was inappropriate, but by that point it was too late to take it back."
The councillors said when they challenged him, he said he was "joking."
They said they did not want the security guard to lose his job however.
Ms Conway added: "Although we've made so many strides in so many senses, it reminds you that there's still so much further to go.
"The assumptions that that security guard had made in that instant - we need to ensure that there's better representation of black and minority ethnic people, and women specifically, in those roles of power and influence in the UK."
Rounding off a social media post on the topic, Ms Conway said, "The struggle continues sisters."
Event organiser London Assembly member Florence Eshalomi has registered a formal complaint about what happened.