Cleaners employed by Interserve at Waterloo Station are holding two 24-hour strikes this week.
The RMT union, which represents the cleaners, says that their grievances include victimisation and dismissal of union members, failure to follow agreed procedures, underpayment of wages and bullying and harassment of staff.
The union also claims that one manager told a member of staff that in their opinion Interserve "should not employ black people".
"The appalling treatment of cleaners at the busy and iconic Waterloo Station is nothing short of a disgrace and has led to a complete breakdown in industrial relations which left RMT with no option other than to ballot for strike action," said RMT general secretary Mick Cash.
"This union has rarely come across a more vindictive and aggressive approach to low-paid staff, doing some of the most under-valued work on our railways, and the situation at Waterloo shames London.
"The overwhelming vote for action shows clearly that this determined and organised group of staff are not going to put up with the outrageous culture of racism, bullying and harassment and they deserve the full support of the entire labour and trade union movement..
"These staff are doing dirty jobs in often appalling conditions and the very least that they can expect is to be treated with dignity and respect. Not only are our members being denied the most basic levels of fair treatment and workplace rights but they are being subjected to a daily regime of bullying, victimisation and harassment which includes disgraceful incidents of racist abuse.
"Interserve, and Waterloo Station itself, cannot sweep this situation under the carpet. RMT is demanding workplace justice for the cleaners at Waterloo and the union remains available for talks aimed at securing that."
An Interserve spokesman said: "We are committed to providing a safe and supportive environment for all our staff and take allegations of this nature extremely seriously.
"We have been working with the union to investigate the issues raised and a formal investigation is underway.
"We are disappointed our employees feel the need to take industrial action, however we have contingency plans in place to minimise any disruption to services."