The bodies of 13 workers at a Peruvian gold mine were discovered over the weekend as criminal groups step up a wave of terror over control of the precious metal in the country’s northern highlands.

The deceased — found in a mine shaft after being kidnapped several days earlier — were working as guards at a small operation that is a contractor to Cia. Minera Poderosa, one of Peru’s largest gold producers. At least 39 workers have been killed in recent years in the gold-rich area of Pataz, the Lima-based metals producer said Sunday in a statement.

The massacre underscores authorities’ struggles to respond to the emergence of violent gangs tapping into Peru’s illegal gold boom at a time of record high prices. Violence has continued in Pataz even after a state of emergency was declared more than a year ago.

While Peru is best known for its massive copper mines, it’s also a significant gold producer. The case is another blow to the already unpopular President Dina Boluarte and to the country’s reputation as an investment destination. SNMPE, the association representing global producers such as BHP Group and Glencore Plc, said the government has yet to even approve a plan to combat illegal mining, which also poses a threat to formal operations.

“The kidnapping and murder of these workers demonstrates that illegal economies seek to intimidate Peruvian society and seize public and private property, such as formal mining concessions and operations,” SNMPE said in a statement late Sunday.

Opposition lawmakers were collecting signatures Monday to potentially censure Prime Minister Gustavo Adrianzen, who last week expressed doubts about whether Poderosa’s contractors had really been kidnapped. It’s unclear whether they will find enough support, but lawmakers have in the past censured several cabinet ministers.

The formal mining industry has been critical of a mechanism designed to allow artisanal miners to formalize their operations, saying it has merely provided quasi-legal status that has helped promote informal mining.

Poderosa also called on authorities to change their security strategy in Pataz province. The sector has suffered from the impacts of illegal activity, including “violence, pollution, and death,” the company said.

The governor of the region where Pataz is located called on Boluarte’s administration to declare martial law in the area.