Tens of thousands of workers at telecoms giant BT walked out on Friday in the first strike of two over pay.

It is estimated that around 40,000 of BT’s U.K. employees, mostly engineers, have walked out.

Staff voted in favour of industrial action after BT offered a £1,500 per year pay rise. BT argued this represents a pay rise of around 5% on average and 8% for the lowest paid. It also said this was “the highest pay award in more than 20 years.”

However, the Communication Workers Union (CWU) equated the offer with a pay cut when taking into account inflation. It has previously criticised the deal, saying company bosses had “stuck two fingers up” to workers.

Friday’s is the first national telecoms strike in the U.K. since 1987. The BT workers plan a 24-hour strike again on Monday.

BT said it has “tried and tested processes for large scale colleague absences to minimize any disruption.”

However, the CWU has warned the BT strikes could affect the rollout of ultra-fast broadband and cause issues for people working from home.

‘They Deserve a Proper Pay Rise’

Prices are rising in the U.K. at the fastest rate in 40 years, prompting workers and unions to call for pay rises to keep up with the cost of living. Several industries, such as the railways, have already seen strikes this summer — and more are planned.

Friday’s strike follows BT’s latest quarterly results. BT announced revenues increased by 1%, to £5.1 billion, for the quarter ending June 30.

The CWU said it “nailed management’s lie that BT cannot afford to pay frontline workers a rise that even comes close to inflation.”

In response, BT said it was “balancing the complex and competing demands of our stakeholders.” That includes making “once-in-a-generation investments to upgrade the country’s broadband and mobile networks.”

BT also said it would not re-open the 2022 pay review.

However, in an angry statement, the CWU pointed to BT’s £400 million profit in the first quarter. CWU deputy general secretary Andy Kerr hit out at the “insatiable greed” of BT’s senior management team.

“Our members kept the country connected during the pandemic. They deserve a proper pay rise, and that’s what they are going to get,” Kerr said.