They will stage two 24-hour strikes as workers walk out over row about money.
It will be the first strike action at BT Group since 1987.
The union said it wanted a “substantial” pay rise, especially with the spiralling rate of inflation, arguing that BT could afford it.
It involves those who look after the majority of Britain’s telecoms infrastructure, from mobile phone connection, broadband internet and back-up generators to national heath systems, cyber security and data centres.
CWU general secretary Dave Ward said: “For the first time since 1987, strike action will now commence at BT Group. This is not a case of an employer refusing to meet a union’s demands – this is about an employer refusing to meet us whatsoever.
“The serious disruption this strike may cause is entirely down to Philip Jansen (BT chief executive) and his friends, who have chosen to stick two fingers up to their own workforce.
“These are the same workers who kept the country connected during the pandemic. Without CWU members in BT Group, there would have been no home-working revolution and vital technical infrastructure may have malfunctioned or been broken when our country most needed it.
“Our members worked under great difficulty and got a real-terms pay cut as a reward. The reason for the strike is simple – workers will not accept a massive deterioration in their living standards.
“We won’t have bosses using Swiss banks while workers are using food banks. We are not going to stop until we win.”
The announcement follows a strike ballot in Jun, which saw 30,000 Openreach engineers voting for action by 95.8 per cent on a 74.8 per cent turnout.
Workers in BT, approximately 9,000 of whom work in call centres, voted to strike by 91.5 per cent on a 58.2 per cent turnout.