When four agency workers – all Latin American migrants – turned up for a shift at Sotheby’s auction house one morning, a man was waiting at the door to tell them they couldn’t come in. The day before, they took part in a union protest calling for a liveable sick pay. The day after, they were suspended from work.

Across the table from me in a Wandsworth café, Dani is still coming to terms with outrage and disappointment nearly one month later. “When I came to London, I didn’t expect this kind of treatment. I came here pursuing a better quality of life. When you find these things, it’s really disappointing. We’ve been treated like criminals when it’s our human right [to protest].”

The protest was peaceful Dani says and police confirm no one was arrested. Dani’s union – United Voices of the World (UVW), which works predominantly with Latin American migrant workers – has dubbed the group ‘The Sotheby’s Four’ and demanded their reinstatement. The battle brought against these four workers is “one big campaign of trade union victimisation” says Petross Elia, the man at the helm of UVW.

Dani and the others are employed by cleaning agency Servest which outsources workers to companies such as Sotheby’s. Right now if Servest employees are sick for one day, they get nothing. If they’re sick long-term, they get just £88.45 per week. The amount is in-line with government requirements but “you can’t survive on that”, says Dani.

Sotheby’s recently reported a decline in profits, but last year they still made $117.8 million (that’s around £76 million) in net income, reports Bloomberg. Servest boasts of clients such as Tesco, Crossrail and the Ministry of Defence; it is one of the UK’s largest cleaning services companies.

Rosa Crawford, international policy officer at the Trades Union Congress (TUC), says: “If the agency says they can’t afford to pay proper wages but we know many are making huge profits, you have to ask ‘where is all the money going?’”

Servest employees feel victimised for union action

Nervously, Dani asks for anonymity, frightened of being identified and further victimised by Servest. I’m shown a letter sent to Dani from the agency. It says Sotheby’s requested that Servest “stop you from working at their site. Their reasons being that the actions taken by you [in the course of the recent protest activity] has disrupted their business and damaged their reputation which has consequently led to a loss of trust in you.”

To Elia, Sotheby’s brazen distain of protest and union membership takes exploitation to “a new level” but for migrant workers in the UK, life is tough. Elia recites an endless list of problems they face: race discrimination; non-payment and under payment of wages; verbal abuse; sexual abuse and dismissal for the most trivial of reasons – he mentions one worker who was dismissed for using another person’s coat hanger.

“Companies feel they can get away with it [with migrant workers] because there is a low density of union membership and a lack of language,” he says.

This is not the first time Dani has felt victimised for union action. Earlier in the year, Dani was among a group of Sotheby’s workers who won the London Living Wage. Twelve employees took part in this campaign but once it ended, the majority chose to leave the union. Only the Sotheby’s Four remained members.

After this campaign, Dani felt bullied by Servest managers. The job was the same but suddenly everything had changed; workloads became excessive and there was constant criticism. It felt like Dani was being punished for being a union member.

“Whatever I did was wrong.” Pressure mounted. “I couldn’t do the job anymore. I was so stressed. It was affecting me physically and emotionally. I was forgetting things. I had to go to my GP.” These were the kind of reasons Dani decided to unionize in the first place. And it wasn’t an unusual problem. “It happened to me, it happened to colleagues”.

“Cleaning companies instil fear in workers,” says Elia. “They want no trouble, resistance, complaints or unions. Companies are always picking off those spearheading campaigns for justice at work.”

A 2014 report by the Equality and Human Rights Commission which examines employment practices in the cleaning sector – a sector where 30 per cent of workers are migrants – echoes Dani’s complaints. It too cites bullying by supervisors and excessive workloads as examples of employment rights not being upheld.

Since Dani’s suspension, that pressure has returned. During meetings with Servest, Dani has had to guard against trick questions. “I’ve been interrogated like I was a criminal but I’ve done nothing wrong. They’ve been asking me about my role in the union.”

Then there’s been the bombardment of letters: “They try to break you down. All these letters have really affected me but I’m not going to let them take away my rights.”

The letters carry with them accusation after accusation. They range from extremism - Elia believes this is because a radical group called Class War attended the protests - to assaulting Sotheby’s clients with water pistols. “How can I be held responsible for the actions of every person at the protest?” says Dani, frustrated.

Outsourcing can impact working conditions and erode labour rights

Elia believes The Sotheby’s Four are victims of outsourcing – when companies choose to use agency workers instead of in-house staff. Outsourcing is supposed to make services more efficient but constant pressures to keep costs low often have a knock on impact on working conditions, particularly for migrant workers who are rarely unionised and less aware of labour rights. Intimidation and pressure from management prevent many from speaking out.

Lucila Granada of charity, the Latin American Women's Rights Service agrees: “They [agency workers] have fewer rights by definition. You are not an employee, you are a worker. When people come to our organisations' employment advice sessions and bring horrible cases of exploitation, the advisers say ‘you can take your employer to a tribunal’. But in many cases if you go against a big agency, you will lose future work and they can't afford that.”

Towards the end of July, UVW celebrated the reinstatement of two of The Sotheby’s Four. However the two others remained under investigation and suspended from work.

In response to allegations, a Sotheby’s spokesman said: “Cleaners who work at Sotheby’s are employed by Servest Group Limited. They are paid the current London Living Wage of £9.15/hour and Sotheby’s fully supports this…. The investigation regarding the two other cleaners is on-going Sotheby’s awaits the outcome of Servest’s investigation.”

A spokesperson for Servest also made a statement: “At Servest we value our employees and respect their rights and entitlements, and we work hard to follow best HR practice at all times. For legal reasons, we are currently unable to comment on the decision by our client to request the removal of employees from their site. We are working to resolve the issue as quickly and as sensitively as possible.”

But after Servest and Sotheby’s gave these statements, the two employees who remained under investigation were told in a meeting they would not be able to return to work. Eila told me the reasons Servest gave were because the pair are “active members of a trade union”. Neither Servest nor Sotheby’s were available to comment on this.

The client-contractor relationship between Sotheby’s and Servest has created a legal no-man’s-land where rights are slipping. The right to protest should be protected by Article 11 of the Human Rights Act but neither company seem willing to be held accountable. Servest say they are carrying out the wishes of Sotheby’s, their client. Sotheby’s, meanwhile, rely on the fact they are technically not the direct employers.

The person interviewed in this article is one of The Sotheby’s Four, however their name has been changed and their gender concealed in order to prevent their identification.