BT workers start voting on Thursday on whether to strike in a dispute over pay.
Ballot papers have been sent out to members of the Communication Workers Union (CWU), with the result expected before the end of the month.
The union said a national strike would be the first since the company was privatised in the mid-1980s.
The CWU has accused BT of attempting to impose an “incredibly low” flat rate pay rise.
BT said it had awarded a £1,500 consolidated pay increase to 58,000 employees, effective from April, including engineers, contact centre and retail staff.
The company said this represented an increase of up to 8% for some workers and more than 3% for the highest paid frontline workers.
CWU deputy general secretary Andy Kerr said: “Today has seen the beginning of a fight for pay dignity.
“As ballots begin dropping through the doors of CWU members, thousands will be thinking of the soaring cost of living, and the insulting treatment they’ve received at the hands of employers.
“While BT Group created even better profits than was expected, many workers who made that profit rely on food banks and don’t know how they will pay their bills.
“The people at the top of BT should be thinking about that as they count their money.
“These key worker heroes are more than owed a proper pay increase – and if they aren’t going to be given it, they’re not afraid to fight for what they deserve.”
CWU general secretary Dave Ward added: “During the pandemic, this set of workers went above and beyond to keep our country going.
“Now, as inflation soars and the bills spiral out of control, the people who generated unexpected profits for BT Group are being hung out to dry.”
A BT Group spokesperson said: “We awarded the highest pay rise we could for team members and frontline colleagues across BT Group. It’s our highest salary increase in more than 20 years.
“So it’s disappointing that the CWU has decided to ballot for industrial action without consulting its members on the outcome of our negotiations. If a strike takes place, nobody wins.”
BT said for a typical field engineer, the pay rise represents around a 5% increase and 7% for contact centre staff.