Unions at French drug maker Sanofi have held a one-day strike at the lab where it is developing a Covid-19 vaccine to protest against job cuts.

Some 200 workers with union flags and megaphones gathered outside the entrance to the Sanofi research and development facility in Marcy l’Etoile in central France They said that hundreds of planned job cuts in France could slow the fight against the coronavirus pandemic.

The company announced last year it plans 1,000 job cuts across France over three years “to reinforce the effectiveness of our organisation and adapt to the evolution of jobs and stakes of tomorrow”.

It said in a statement that it would rely on voluntary departures, but would not comment further because of confidentiality rules amid ongoing negotiations with unions.

Union members at Sanofi also plan to join broader demonstrations on Saturday in France against job cuts during the pandemic.

Sanofi, France’s biggest pharmaceutical company and a world leader in vaccine development, has also come under criticism for its slow Covid-19 vaccine rollout.

Sanofi and British partner GlaxoSmithKline said last month that their potential vaccine will not be ready until late 2021 because they need to improve the shot’s effectiveness in older people.