Polish police are investigating an abattoir suspected of illegally trafficking in sick cattle, which has been filmed covertly.
Poland's chief veterinary officer says the film, broadcast by Polish TVN 24, reveals "illegal activities, as slaughter was carried out deliberately at night, in order to avoid official supervision".
The film shows visibly sick cows, and abattoir workers cutting carcasses.
It is not clear where the meat went.
The revelation is potentially serious for the EU, because in 2013 a horsemeat scandal exposed the complexity of meat sales in Europe's single market.
The scandal triggered product recalls, as officials struggled to trace suspect meat.
The veterinary officer's statement says his inspectors and police were tipped off about "suspected illegal slaughter" at an abattoir near Ostrow Mazowiecka in north-eastern Poland.
On the night of 14-15 January they found eight sick cows there and "a decision was made to kill the animals without delay in order to end their suffering".
"During the check, the owners of the animals were identified, along with an animal dealer who transported cattle unfit for transport, and abattoir staff responsible for animal welfare there," the statement said.
The statement came days after the TV broadcast, which showed cows that were too sick to stand being dragged from lorries into the slaughterhouse.
The inspectors have been ordered to check other abattoirs in the region and police are trying to identify any buyers or sellers of meat from sick animals, which is unfit for sale.
The EU statistics agency, Eurostat, says Poland is the seventh-largest producer of cow meat in the EU, based on slaughterhouse data.
In 2017, it produced some 558,500 tonnes of beef and beef products. That puts Poland behind (in ascending order): Ireland, Spain, Italy, the UK, Germany and France.
Poland produces almost two million head of cattle a year for slaughter.
However, beef makes up just 2% of meat consumption within the country, according to international conference organisers ITE Group plc.
UK Revenue and Customs (HMRC) data shows that in 2017 the UK imported £64.4m ($85m) worth of Polish beef - about 16.5m kg.
Polish beef exports to the UK are roughly the same as those from the Netherlands. Ireland is a much bigger beef exporter to the UK: in 2018 it provided some £723m worth.