(Yicai Global) Jan. 7 -- Shares of China's STO Express tumbled to a more than six-year low after the logistics firm refuted its former employee's claim of compulsory overtime.

STO Express's stock price [SHE: 002468] closed 5.1 percent down at CNY9.51 (USD1.50) today, after touching CNY9.41, the lowest since the third quarter of 2014.

An insider at the courier firm said to news outlet Sina Tech today that the ex-worker's description of the incident is inconsistent with the facts. The company has not made a public statement.

The Shanghai-based firm had been ordered by a local labor arbitration commission to compensate the former employee, surnamed Jiang, for his contract termination that was deemed illegal, Feidian Video under mobile news aggregator Yidian Zixun reported yesterday. STO Express has appealed the ruling.

After a bit more than two months since joining the company, the recent graduate had been told on Sept. 9 that he has not passed the probation. The reason was that Jiang had refused to work overtime, based on his claim.

A deputy director had asked a team to stay at the office till 9 p.m., according to Jiang. The executive had warned the workers against pursuing romantic relationships within five years since graduation, according to an audio recording.

Many netizens have proceeded by writing posts on the logistics firm's Weibo feed, pondering how the strenuous '996' working culture has become a norm for young workers that is hard to break free from as it is often encouraged by executives.

The incident comes only days after it was widely reported in China that a 22-year-old employee at Pinduoduo had passed away after collapsing on her way home from work after 1 a.m., shining a light on the notorious but unwritten rule of the 9-to-9-six-days-a-week schedule at some Chinese tech firms.

Editor: Emmi Laine