More than 30,000 employees at BT and its Openreach broadband arm today voted overwhelmingly in favour of taking industrial action in a row over pay.
If strikes go ahead, they would be the first across BT for 35 years, and since the privatisation of the firm.
BT staff became the latest workers threatening to walk out in what is set to be a summer of discontent.
They are angry after the telecoms giant imposed a salary rise, said to be worth £1,500, without consulting their union.
Openreach members voted 95% in favour of strikes and BT staff by 91%.
They include call centre workers and broadband engineers.
The Communication Workers Union said it wanted to hold new talks with BT.
But general secretary Dave Ward warned any strikes could have a “very significant impact”. An unnamed Openreach worker said “morale is very low”, claiming experienced staff on higher pay were being replaced with new recruits on £10,000 to £15,000 a year less.
They warned: “On any given day, you are looking at thousands upon thousands of faults that need to be fixed.
“If they’re not fixed then households and businesses don’t have broadband.”
Mr Ward said those voting to strike were key workers during the pandemic, enabling the home-working revolution.
He added a key reason for the disputes was “the deep imbalance of wealth”.
BT said it awarded its highest pay rise for frontline staff in more than 20 years – an average 5% hike and up to 8% for those on the lowest salaries.
It added: “Our job is to balance the competing demands of stakeholders, especially in a challenging economic environment.
“The result of the CWU’s ballot is a disappointment but we will work to keep customers and the country connected.”