Internet users who allegedly illegally shared or downloaded the film Ava are being threatened with legal action.
Internet providers were forced to reveal customer names and addresses following a court order issued on behalf of Voltage.
It is the first time in years that rights holders have used these methods to seek redress for piracy.
It comes as UK police arrested three people accused of running an illegal streaming network.
The practice of sending letters to those identified as having downloaded illegal content is not without controversy, because the threats of legal action are rarely taken to court.
That is because any case would rely on an IP address, which often cannot be used as a reliable means of identifying an individual - at least not without an admission of guilt or an inspection of computers or hard drives owned by the suspect.
Virgin Media, one of the ISPs that has been forced to identify customers, told the BBC: "We take the privacy and security of our customers' data very seriously and will only ever disclose customer information to third parties if required by law to do so through a valid court order.
"Any customers who receive a letter should note that the court has not yet made any findings of copyright infringement against them. This would be a matter to be determined by the court in any subsequent claim."
The film in question, Ava, was released in 2020, and starred Jessica Chastain and Colin Farrell.
The letter, sent by law firm Lewis Silkin LLP on behalf of rights holder Voltage and seen by news website Torrent Freak, offered the person the opportunity to "admit or deny that your broadband account was used via BitTorrent in relation to Ava".
It goes on to say that the onus would be on Voltage to prove these allegations in court and suggests users instead "pay a reasonable sum by way of compensation".
Separately, police in the West Midlands have arrested three people suspected of running a huge illegal streaming network.
A 40-year-old woman and two men aged 53 and 35 are suspected of providing illegal content to more than 100 separate pirate TV services, believed to serve hundreds of thousands of customers.
The network, which was shut down, included a large catalogue of live TV and video content from around the world, including sports, for use on smart TVs, phones and tablets, police said.
Fact (Federation Against Copyright Theft) issued a warning to people running such networks and those watching them: "Users and subscribers of illegal services should be aware that not only are they committing an offence themselves, but they're also exposing themselves to risks including identity theft, malware and viruses."