Operators who handle 999 emergency calls are set to join a BT Group walkout on Thursday.
The Communication Workers Union (CWU), which represents BT workers, had previously agreed to exempt 999 staff from the strike action – but had changed its position after “widespread outrage at the company’s refusal to negotiate”.
Further walkouts are currently planned to take place on 10, 20 and 24 October amid warnings of what could be a “dangerous dispute for many”.
Around 500 emergency call handlers will walk out for the first time as they join their colleagues.
BT told Sky News it has “up to 150 call handlers on shift at any one time in our 999 contact centres and we would look to maintain those levels by redeploying colleagues”.
The company added it will have “experienced agency teams” working on strike days and “expect a number of our colleagues” will also attend work as normal.
It has also “been training colleagues” to “fill gaps from any absences”.
The strikes are set to include the 30,000 Openreach engineers and 10,000 BT call centre workers who have taken action in previous months.
Action has been taken in opposition to BT Group management’s offer of a flat-rate pay rise of £1,500.
BT said it awarded a pay increase to its team member and frontline colleagues of £1,500, which it said represents a pay rise of around 5% on average and 8% for the lowest paid.
‘999 operators are using food banks’
The CWU said in the context of RPI inflation levels already hitting 11.7% this year, the offer is a “dramatic real-terms pay cut”.
CWU general secretary Dave Ward said “repeated attempts to initiate discussions” was declined by “a management who clearly believe they are above negotiating a fair deal for people who make massive profits for them”.
He added: “999 operators are using food banks, they’re worried about the cost of living and are being stretched to the limit.”
CWU deputy general secretary Andy Kerr said: “Time and time again we have asked for negotiations to resolve what may well be a dangerous dispute for many, only to be ignored by a senior management that could not be less interested in addressing the anger that exists in their workplaces.”
Read more on Sky News:
Royal Mail workers to strike on 19 days
How would a squeeze on benefits affect people?
A BT Group spokesperson said: “We know that our colleagues are dealing with the impacts of high inflation and, whilst we respect the right of colleagues to take industrial action, we are profoundly disappointed that the CWU is prepared to take this reckless course of action by including 999 services in strikes.
“We will do whatever it takes to protect 999 services – redeploying our people to the most important priority is a normal part of BT Group operations.
“We made the best pay award we could in April and we have held discussions with the CWU to find a way forward from here.
“In the meantime, we will continue to work to minimise any disruption and keep our customers and the country connected.”