A week after Japanese regulators postponed the restart of the world’s biggest nuclear power plant due to safety lapses, a careless employee working from home added to the company’s woes.

Tokyo Electric Power Co., which operates the Kashiwazaki-Kariwa nuclear power plant in Japan’s Niigata prefecture, said an employee placed a stack of documents on top of a car before driving off and losing them.

The mishap is the latest in a string of mistakes for the utility and is likely to further erode the regulator’s confidence in Tepco. Safety lapses and a strict regulatory process have stopped Japan from restarting most of its nuclear reactors shut in the wake of the 2011 Fukushima disaster.

The nation’s Nuclear Regulation Authority, which oversees safety protocols of Japan’s remaining 33 nuclear reactors, decided just last week to keep a de facto ban on the power station from resuming operations, saying that the utility’s preventative measures are inadequate.

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Some of the papers were recovered by a local resident, Tepco said, adding that 38 pages were still unaccounted for. Tepco said it has warned its staff and management and will make sure all employees follow stringent rules on taking documents and information off-site.