Investors and lawmakers are putting pressure on T-Mobile’s parent company Deutsche Telekom to review the working conditions of its employees in the United States, Reuters reported.

The pressure comes amid allegations by the Communication Workers of America (CWA) that T-Mobile’s rapid expansion has come at the cost of employees’ rights and rulings in National Labor Relations Board (NLRB) cases that found T-Mobile to be engaged in illegal work practices.

In the NLRB cases, T-Mobile was found to be in violation of NLRB regulations with policies that prohibited call center employees from discussing their working conditions with the media and barred employees from sharing their compensation information with one another. T-Mobile’s strictly confidential internal investigation practices were also found to be at fault.

In total, 11 of T-Mobile’s employee practices were found to be illegal.

In response to the March NLRB rulings, a T-Mobile spokesperson said “This is simply a ruling about a technical issue in the law that relates to policies that are common to companies across the country.  There are no allegations that any employee has been impacted by these policies.”

In light of the accusations and rulings, however, Deutsche Telekom’s shareholders – including APG Asset Management and Norges Bank Investment – have called for the company to ensure proper worker treatment. In 2011, APG removed Wal-Mart from its portfolio, citing concerns over working conditions at the retail giant.

Members of the U.S. Congress have also asked the German government, which controls 30 percent of the company, to apply pressure on the company to ensure workers’ rights are upheld.