Board members meanwhile vowed to sue the company for tracking their calls, a financial newspaper accused it of spying on its staff and the current chief executive looked in danger of becoming implicated in the affair.
Deutsche Telekom at the weekend conceded that it had hired detectives to track hundreds of thousands of phone calls by senior executives and journalists to identify the sources of press leaks.
On Thursday, staff representatives on the company's supervisory board said they assumed they were "the first victims" in the affair and have decided to sue the company for violating their privacy rights.
"We have decided to take legal action," said the deputy president of the board, Lothar Schroeder, who represents the Verdi trade union.
Deutsche Telekom admitted on Saturday that it had made "ill-advised use of communications data" in 2005 and probably 2006.
It has so far admitted only to targeting the magazine Capital but on Thursday the Financial Times Deutschland alleged that it was also a victim of espionage by Deutsche Telekom and as early as 2000.
The daily said in a front-page report that Deutsche Telekom had hired private detectives to spy on its reporters eight years ago and had even secretly filmed the newsroom.
"Their main target was the FTD's chief reporter at the time, Tasso Enzweiler, who often broke stories about the telecommunication sector.
"The private detectives even used a hidden camera to try and get information about Enzweiler's source from the newsroom in Cologne," the newspaper said.
Both the FTD and Capital belong to the publishing house Gruner und Jahr, which is turn is owned by German media giant Bertelsmann.
The publisher has warned that it is considering both criminal and civil charges against Deutsche Telekom.
The telecoms giant insists that the Berlin consultancy firm it hired had not listened to journalists' conversations but only logged details on who phoned whom as well as the time and duration of the calls.
The scandal is proving deeply damaging in a country already nervous about "Big Brother" style privacy invasion and chief executive Rene Obermann has embarked on a damage control campaign.
Obermann announced that state prosecutors and a law firm in Cologne were investigating the affair and promised Deutsche Telekom users that they were not being wiretapped.
The "personal data of our millions of fixed-line and mobile clients was secure," he told Germany's top-selling newspaper Bild.
Though Obermann only took over the reins at Deutsche Telekom in November 2006, pressure is growing on the chief executive to explain his role in the affair.
A company statement issued Thursday hinted that he learnt last year that a Capital reporter had been under surveillance in 2005, when predecessor Kai-Uwe Ricke had been in charge.
The board was informed of the case, the statement said, but decided to keep quiet because "in the end Mr Obermann must act in the interest of the company."
Deutsche Telelom is the latest in a string of major German companies to be hit by revelations that it spied on its own staff.
In the highest profile case, it emerged in March that discount food retailer Lidl had hired detectives to install micro cameras that filmed employees while at work and on their breaks.
Lidl recorded employees when they used the toilet, their conversations while on breaks and even kept track of who their friends outside work were, reports said.