Omari Smith said a 5.5 per cent pay offer from Royal Mail had come with strings attached, including mandatory Sunday working, shorter working weeks in the summer to bank longer weeks in the winter and later starting and finishing times.
Communication Workers Union (CWU) general secretary Dave Ward said 115,000 members were striking over pay amid ‘rocketing’ inflation and energy bills.
He declared Friday’s industrial action as “the biggest strike in the UK since 2009”.
Mr Ward said his members voted in favour of the strike by 97.6% in a ballot, after management “imposed” a 2% pay rise on employees but “rewarded themselves with record bonuses”.
Friday’s strike will be followed by further stoppages on Wednesday August 31, Thursday September 8 and Friday September 9.
On Thursday, a Royal Mail spokesperson said: “Tomorrow’s CWU strike thrusts Royal Mail into the most uncertain time of its 500-year history.
“It is putting jobs at risk and making pay rises less affordable. We are losing £1 million a day.