A Deutsche Telekom spokesman partly confirmed press reports that the group had gone through the bank records of more than 100,000 workers in 2006 and compared them with those of suppliers for signs of potential shell companies.
The telecoms operator called the move a "test" and declined to give the exact number of staff that had been checked up on. In April, Deutsche Telekom acknowledged that it had also looked into the activities of supervisory board members to determine if they were the source of press leaks.
The group now stresses the information gathered was treated in an anonymous way by internal agents and that personnel representatives were duly informed. The scandal at Deutsche Bahn is more volatile, in part because the company has only released information sparingly and also owing to the confrontational stance of its boss, Hartmut Mehdorn.
On Wednesday, the state-owned rail operator confirmed that in 2005 it had scoured the personal data of 173,000 workers, around three-fourths of its workforce, for signs of dubious coincidences with suppliers.
The company acknowledged last week following reports in the media that similar operations had taken place in 2002-2003 under the code names "Babylon" and "Squirrel" by a group of private detectives, without the unions' knowledge. Mehdorn told workers in a letter he had made "mistakes," but insisted his actions were irreprochable from a legal point of view.
An expert in domestic politics for the Social Democratic Party (SPD), Dieter Wiefelspuetz, told the Kölner Stadt-Anzeiger newspaper in an interview that "Mehdorn should perhaps begin to look for another job."
At the Transport Ministry, a spokesman pressed Deutsche Bahn to explain its actions without delay, but added that "the time has not yet come to speak of personnel consequences." Chancellor Angela Merkel's spokesman refused to say whether she still had confidence in Mehdorn.
Meanwhile, Deutsche Bahn has become the focus of criticism by specialists in the protection of private data.
To fight corruption, "you must respect certain rules, by alerting trade unions and basing your actions on concrete suspicions for example," said Thilo Weichert, who handles data protection issues for the northern German state of Schleswig-Holstein.
Labour law professor Peter Wedder added that "coming from Deutsche Bahn, a publicly-owned company, it sends a disastrous signal to the private sector."
Weichert told AFP that "the question of private data confidentiality is a particularly sensitive one in Germany. That is a result of our experience with dictatorships, both Nazi and communist."