(Adds government comment)
LONDON, Oct 15 (Reuters) - Thousands of postal workers will stage two days of strikes next week, their trade union said on Thursday, in a dispute over pay, jobs and modernisation at Britain's state-owned Royal Mail.
Royal Mail's Managing Director Mark Higson called the decision an "appalling and unjustified attack on customers."
A strike would cripple deliveries across the country and could cost the economy an estimated 1.5 billion pounds ($2.4 billion), retailers have said.
The CWU said 42,000 mail centre staff and network drivers would strike on Oct. 22 and 78,000 delivery and collection staff would walk out on Oct. 23.
The government said ndustrial action was the last thing the service needed.
"Candidly, I think it is suicidal. It will only serve to drive more customers away from Royal Mail," said Business Secretary Peter Mandelson.
The Communication Workers Union (CWU), which acts for 120,000 UK postal workers, said it had "no choice" but to announce strike dates after its latest offer was turned down.
Workers voted overwhelmingly last week for nationwide action, escalating a dispute which has already caused widespread disruption to postal services.
(Reporting by Stefano Ambrogi; Editing by David Cowell)