Hundreds of workers at the Hinkley Point C nuclear construction site in Somerset have staged a wildcat strike in protest against alleged bullying by the project’s supervisors.

A group of mechanical engineers numbering in the low hundreds downed tools on Tuesday without the backing of their trade unions amid deepening woes within the 26,000-strong workforce over the conditions on the site.

It was the second unofficial strike to take place in a week after a walkout last Wednesday in defiance of union reps and the site developer, French utility company EDF, following claims that senior managers on the Hinkley site have bullied engineering staff.

A contract worker on the project, which is running years late and billions of pounds over budget, told the Guardian one of the incidents was believed to have involved a senior manager bullying a young woman on the team.

“They’ve had enough, and they’re out the gate,” he said.

Trade union Unite confirmed that a number of workers are taking part in a protest over “management practices” which has resulted in the workers being removed from the site. “Unite expects this matter to be resolved soon,” a spokesperson said.

The Guardian understands that EDF, which is developing the first new nuclear reactor in a generation at Hinkley Point, has begun an independent investigation into the alleged bullying on site.

The row has emerged days after the UK nuclear watchdog confirmed it would prosecute EDF alongside the site’s main contractors Bouygues Travaux Publics and Laing O’Rourke for health and safety offences over the death of a site supervisor at the site after an accident in 2022.

Workers have also reportedly complained that the construction site is overrun by rats. The Unite and GMB trade unions are understood to have warned EDF that urgent action is needed because the rodents are “everywhere”.

A spokesperson for Hinkley Point C said: “We join with our trades union partners in asking that the correct process is followed to resolve any grievance. Normal working throughout the site has been unaffected by this unofficial action.”