Private spies reportedly infiltrated an Amazon strike, secretly taking photos of workers, trade unionists, and journalists. Now a union is taking legal action.

Private spies subcontracted by Pinkerton Agency, a firm Amazon employs, infiltrated and photographed a worker strike at a warehouse on Black Friday in 2019, a Spanish media outlet reported.

The spies compiled a 51-page document, which included photos of trade unionists, workers, and journalists who attended the strike, El Diario reported.

Amazon has used Pinkerton spies to track warehouse workers and labor movements at the company in the past, according to a November report.

The Spanish labor union CCOO has asked a judge to seize documentation relating to the report and said it was considering legal action against Amazon. An Amazon spokesperson told El Diario the e-commerce firm had not instructed Pinkerton or any other agency to spy on the strike.

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Amazon could face a court battle with a Spanish workers' union over a report that said private investigators were hired to infiltrate and secretly surveil a strike outside one of its warehouses.

According to a 51-page document obtained by the Spanish news site El Diario, private detectives spied on an Amazon workers' strike at a warehouse near Barcelona, Spain, on Black Friday in 2019. The strike was part of a broader freight workers' strike in the province of Catalonia.

El Diario reported that the private detectives who compiled the document were employed by a Spanish company called Castor & Polux, which had been subcontracted by the Pinkerton Agency. A November Motherboard report said Amazon employed the Pinkerton Agency to monitor union activity across Europe.

The document contained photographs of trade unionists, workers, and even journalists who attended the strike, according to the El Diario report.

An excerpt from the document reads: "We saw a group of people meeting, who could be seen wearing CCOO and UGT union bibs/vests. They're recorded for possible identification at subsequent events." This was accompanied by a photograph.

Castor & Polux declined to comment when contacted by El Diario, citing client confidentiality. An Amazon spokesperson told El Diario the e-commerce firm had not instructed Pinkerton or any other agency to spy on the strike.

Amazon and the Pinkerton Agency did not respond to a request for comment. Castor & Polux did not immediately respond to Business Insider's request for comment.

The Spanish labor union CCOO on Tuesday announced it planned to bring legal action against Amazon. Ricard Bellera, CCOO's secretary for work and economy in Catalonia, told Business Insider the union had asked a judge to seize both the 51-page report covered by El Diario and any documents showing any agreement between Castor & Polux and Amazon.

"CCOO wants to know if Amazon carried out, through a contracted company, exhaustive monitoring of people, photographs, and prepared reports of workers and trade unionists of CCOO. The union will assess with its legal services the filing of a criminal lawsuit against Amazon," the union said in a press release.

It added that if the report is proved true, it would mean Amazon broke Spain's constitutional laws on right to assembly and data privacy.

This isn't the first report of secret operatives infiltrating an Amazon warehouse.

Motherboard reported Pinkerton agents were deployed inside a warehouse in Poland in 2019 to investigate whether management was coaching candidates on how to complete job interviews. At the time of the report, Amazon spokesperson Lisa Levandowski told Business Insider that the company partnered with Pinkerton to "secure high-value shipments in transit," not to gather intelligence on warehouse workers, and that all activities are "fully in line with local laws."

Christy Hoffman, the general secretary of the international UNI Global Union, told Business Insider in a statement that Amazon was "using its immense power and resources to snoop on workers looking to improve their jobs."

"As bad as spying on workers is, it doesn't come in a vacuum. There's a pattern here — Amazon's enormous appetite for growth is bad for our societies. This is why on Black Friday more and more people who believe in the dignity of work and the politics of the common good went on strike to stand up to Amazon and demanding change," she added.

This year on Black Friday, Amazon workers and activism groups in 15 countries staged protests against the company to demand better pay and benefits, an end to worker and union surveillance, and commitment to sustainability under the slogan "Make Amazon Pay."