The turbine manufacturer could be planning to close the production sites at Trampe in eastern Germany and Husum in northern Germany.
The workforce in Trampe has observed that key workers are leaving and materials destined for the works there have been redirected elsewhere.
This could lead to work drying up at Trampe with the site closing as early as mid to end of May 2017, Peter Ernsdorf, trade union official for IG Metall Ostbrandenburg told Windpower Monthly.
The Trampe factory produces 3MW machines, while the Husum site makes 2MW turbines, which can also be produced at a Portugal facility.
"It looks as though the company may be considering relocating the Trampe work to the Senvion site at the port of Bremerhaven, and the work from Husum to a Senvion factory in Portugal," Ernsdorf said.
He added: "Senvion, a clean energy company, may not be following fair procedures in connection with consultation with the Works Councils," and pointed to the potentially large impact on local employment at Trampe and Husum.
A Senvion spokesman told Windpower Monthly these claims are rumours that the company has not confirmed.
"All Senvion's production works are under continual monitoring as to their productivity and workload. For years, management has been weighing up the situation at the Husum works and always supported the production locations in Germany," the spokesman said.
There is to be a major Senvion meeting in Hamburg on 13 March and the manufacturer's management will be holding a roadshow in London on 16 March where these issues will be talked about.
"Prior to then no information will be available," the spokesman added.
Another industry source suggested the size of the planned meeting in Hamburg signals a major restructuring could be in the offing, possibly including service, and research and development.