Mainland China’s market regulator has imposed record fines on e-commerce and food delivery giants, amid a background of intense competition that authorities said led to violent resistance to probes.

The 3.6 billion yuan (£390m) in fines across seven platforms run by PDD Holdings, Meituan, JD.com, Alibaba Group Holding and ByteDance were justified by the most severe violations since the adoption of China’s food safety law in 2009, the State Administration for Market Regulation (SAMR) said.

PDD also operates international shopping site Temu, which also known for cut-rate prices and questionable business practices.

The probe was marked by subterfuge and violent clashes, including a company with a hidden office, broken bones and an employee swallowing a note in front of investigators.

During an on-site probe of a site belonging to PDD-owned shopping site Pinduoduo in December, regulators discovered a hidden office area as employees departed for the day, according to a Monday report by China Quality Daily, which is supervised by the SAMR.

As investigators tried to enter the hidden office, an employee crushed the hand of official Guo Hui in a door as he forced it shut, the report said.

The following night, a group led by PDD’s chief of security stormed the site where the investigation was taking place, shoving officers to the ground, resulting in investigator Guo being sent to hospital with a head injury, China Quality Daily‘s report said.

During a formal inquiry with investigators, local police and market regulators, a PDD employee was caught sending notes to a colleague under questioning, with orders such as “Silence” and “Don’t speak”, the report said.

When caught, the employee reportedly crumpled the note and swallowed it in front of officials.

China Quality Daily did not name PDD, but the company was specified in a Saturday report by Xinhua News Agency.

The investigation was prompted by customers who reported substandard bakery items, such as a birthday cake with inedible decorations.

The probe uncovered more than 67,000 unlicensed bakeries operating across the seven platforms, providing goods at cut-rate prices through intermediaries.

PDD said on Friday it “sincerely” accepted the penalty and would improve operations.

Chinese regulators have repeatedly warned against “race-to-the-bottom competition” as food delivery firms compete for customers.