Thousands of BT workers have voted to go on strike in a dispute over pay.
Some 30,000 Openreach engineers and 9,000 BT call centre workers were balloted and overwhelmingly backed industrial action, the Communication Workers Union (CWU) said.
General secretary Dave Ward said BT now faced its first national strike since it was privatised in the 1980s.
BT said it was disappointed and would "work to keep our customers and the country connected" if staff walked out.
Mr Ward said he expected BT to offer a "significantly improved" pay rise by next week or strike dates will be set.
CWU said the potential strike action would have a serious effect on the roll-out of broadband and could cause big problems for those working from home.
Prices are rising at their fastest rate with UK inflation at a 40-year high of 9.1%.
Higher costs for food, unprecedented energy bills and soaring fuel prices are putting households under pressure and workers and unions are pushing for pay rises to help them cope.
But the government has warned against bosses giving big wage increases for fear of causing a 1970s style "inflationary spiral", where firms hike wages and then pass the cost on to customers through higher prices.
This year BT gave staff a £1,500 per year pay rise but CWU said that with price rises at record highs "this is a dramatic real-terms pay cut".
It said BT made £1.3bn in annual profit and the company's chief executive, Philip Jansen, received a £3.5m salary - a 32% increase.
A BT Group spokesperson said the company had awarded its highest pay rise for frontline colleagues in more than 20 years - an average 5% increase and up to 8% for those on the lowest salaries.
It said it was in the middle of a once-in-a-generation investment programme to upgrade the country's broadband and mobile networks which was vital for millions of customers and the UK economy.
"Above all, [the investments] are central to the success of this business - and its colleagues - now and in the future," they said.
The CWU announced that on a 74.8% turnout, the union's 30,000 Openreach engineers voted by 95.8% to take strike action.
It said BT staff, including 9,000 call centre workers, voted by 91.5% on a 58.2% turnout for strike action.
A vote by CWU members at EE failed by a few votes to reach the legal threshold.