The UK's Rail, Maritime and Transport (RMT) union has sought an urgent meeting with Deutsche Bahn (DB) and Arriva subsidiaries.
The RMT is concerned that the £1.59bn ($2.4bn) takeover of the Arriva transport group by DB could create a pan-European private transport monopoly.
RMT general secretary Bob Crow said a private monopoly of rail and bus services across Europe could place profit ahead of safety and service.
Britain’s biggest specialist transport union claimed that its first priority is to protect jobs and conditions of workers.
DB already manages Chiltern Railways and the newly privatised Tyne and Wear Metro.