Deutsche Telekom is facing pressure from investors and lawmakers following growing concerns over working conditions at its American business, T-Mobile US, according to Reuters.

T-Mobile US, which has approximately 45,000 employees, has seen its business expand rapidly over the past two years and in August 2015 overtook long term rival Sprint, to become the third largest operator in the US by connections.

The issue however could somewhat sour some recent positives for the company.

Working conditions of T-Mobile US employees first came into the spotlight last year, after the Communications Works of America (CWA) union accused the company of breaching employee rights, following two US National Labor Relations Board (NLRB) cases which found in March the company had engaged in illegal working practises.

Reuters reports two of the company’s investors have since expressed concern about the treatment of its workers, with pension fund manager APG Asset Management requesting an update on the issue, in light of rulings from NLRB and CWA allegations.

APG, which owns a 0.15 per cent stake in Deutsche Telekom, removed US retailer Wal-Mart from its portfolio in 2011, citing working conditions.

Norges Bank Investment Management, which owns a 1.6 per cent stake in the company, has also expressed concerns, according to sources.

In the first NLRB case, it found the company breached 11 violations, including a ban on employees discussing wages with colleagues and speaking to the media about their working environment. T-Mobile US accepted decisions on nine of the 11 violations.

In the second, NLRB said the company had a policy to prohibit staff in call centres in South Carolina and Maine from talking to colleagues about employment condition, as well as asking workers to sign confidentiality agreements during internal investigations, which were both deemed illegal.

CWA too highlighted several allegations of mistreatment of employees in a report published on July.

Political pressure
Lawmakers in Berlin and Washington are now reportedly calling on the German government, which owns a 30 per cent stake in Deutsche Telekom, to apply pressure on the operator to improve worker rights.

The issue has already caused something of a political storm in Germany.

25 members of the US congress sent a letter to German Chancellor Angela Merkel asking her to look into the matter, while German trade union Verdi also organised a petition on the German parliament website, drawing 50,000 signatures, demanding the finance ministry ensure workers’ rights are upheld.

T-Mobile US reportedly said it abides by the law and denies mistreating workers.