(Reuters) - Britain's Communications Workers Union (CWU) is to ask the High Court in London on Thursday to allow its members working at Royal Mail (L:RMG) to go ahead with a strike, the union said on Wednesday.
Royal Mail on Monday applied to the High Court for an injunction to prevent any strike action being taken before an agreed mediation process for settling labour disputes has been exhausted.
"In light of Royal Mail’s legal challenge we can confirm that the union will be defending its case at the Royal Courts of Justice ... on Thursday," CWU said in an emailed statement.
A court document showed that the hearing for the case - IHQ17/0473 Royal Mail Group Ltd v Communication Workers Union - is scheduled to be heard at 0930 GMT on Oct. 12.
"We believe any strike action before the dispute resolution procedures have been followed would be unlawful strike action," a Royal Mail spokesman said in an email.
CWU and Royal Mail have been embroiled in a dispute over the British postal company's plans to replace its defined benefit pension scheme, a move intended to prevent its annual contributions from ballooning to over 1 billion pounds by 2018.
Around 90,000 Royal Mail workers are in the plan, whose closure to new members in 2008 resulted in about 40,000 workers joining a less generous defined contribution plan.
CWU, which has over 100,000 members in Royal Mail, has argued that company's move to replace the scheme would result in members losing, on average, up to a third of their future pensions.
Both sides have failed to agree on new pension terms since April, and CWU said last week that members would start a 48-hour strike on Oct. 19 that analysts and experts say could cause major disruptions to deliveries.
The pension battle comes as Royal Mail is trying to modernise its business. After years of underinvestment, the former monopoly was privatised in 2013 and has since reduced layers of management, upgraded technology and cut its property bill.
However, it was left struggling last year as its domestic parcels business faced increased competition and as uncertainty following Britain's vote to leave the European Union accelerated the rate of decline in its letters business.
The company's shares, which have fallen 17.2 percent this year, were up 1 percent at 387 pence at 1452 GMT.
(This version of the story refiles to remove extraneous apostrophe in headline.)