T-Mobile’s US executives have told its controlling shareholder, Deutsche Telekom, that they no longer support a proposed $300 billion merger between the two companies, citing both shareholder and potential regulatory concerns, according to people familiar with the matter. Some of T-Mobile’s non-controlling shareholders — generally large institutional investors — have told the US company that they would oppose a merger with Deutsche Telekom, the people said, a slower-growing business compared to its American counterpart. Deal talks between T-Mobile and Telekom kicked off earlier this year and the two companies planned to put a deal to a vote in order to secure the approval from T-Mobile’s non-controlling shareholders, one of these people said. But now, T-Mobile executives aren’t confident the deal would be approved by those shareholders, that person said.