The union spat will add to the problems facing Mr Jansen, who is leading the company at a time when its top brass remain divided over strategy.
Earlier this month Mr Jansen reportedly issued an ultimatum about BT’s direction that sparked the departure of Jan du Plessis from the chairman role.
He announced his resignation last week after failing to bridge the gap between two camps who disagree over the pace of change needed at BT.
One group of directors, including Mr Jansen, wants BT to accelerate decisions around its nationwide broadband network Openreach, as well as restructuring.
However, other board members want more certainty around external issues such as regulation, according to insiders.
Mr Jansen threatened to resign if the board did not find a chairman who would accelerate change, after clashing with Mr du Plessis over issues including the potential sell-off of Openreach, Sky News reported.
Mr du Plessis is understood to have believed it was too early to bring in an outside shareholder into the ownership structure of Openreach, BT’s most valuable asset. But Mr Jansen believed doing so could boost BT’s share price and help fund the national broadband upgrade.
BT did not deny Mr Jansen made such a threat, but a spokesman said: “There has been no misalignment between the board and executive management over the company’s strategy.”
Mr Jansen is also be awaiting a decision from Ofcom that will lay the groundwork for a new regime for the UK’s fibre networks.
Ofcom is expected to introduce price controls on fibre broadband until 2031 in a move that will give certainty to BT’s plans to invest heavily in its own gigabit broadband network.
