Cleaners working on the railways in Kent are beginning an 11-day strike over pay.
Cleaning staff employed by contractor Churchill are walking out as part of their ongoing fight for a £15-per-hour rate of pay.
Currently cleaners working on Southern, Southeastern and Eurostar services can earn as little £8.91 an hour.
The RMT union is also demanding company sick pay and free travel for cleaning staff across the network, in line with other workers on the railway.
RMT general secretary Mick Lynch said: "Churchill have shown a complete disregard for key workers who were rightly considered heroes in the pandemic.
"With the profits Churchill makes, they could easily pay our members a fair wage, pay company sick pay and allow free travel across the network, just like directly employed railway staff.
"But Churchill have offered nothing meaningful to in our pursuit of pay justice.
"RMT will continue to ramp up its campaign and ensure that these greedy multimillion pound contractors are stripped of their ability to exploit workers on our railways."
Cleaners previously staged a one-day strike in February in the fight over pay.
Despite the division of Churchill employing the cleaners making a profit of more than £11m last year, staff are only paid the minimum wage.
They have been left fuming after having to undertake extra tasks during the pandemic to keep up with strict hygiene requirements.
The RMT argues the profits could have been gone towards upping wages for the cleaning staff.