(Reuters) – Britain’s Royal Mail (RMG.L) will use all legal options at its disposal to halt a strike by postal workers this month, it said on Thursday after the industry union announced the action over a pensions dispute.

The Communications Workers Union (CWU) said the 48-hour strike would begin at 1000 GMT on Oct. 19 and would involve about 111,000 postal workers.

Royal Mail said it is committed to further talks to reach an agreement as a matter of urgency but that there are no grounds for industrial action.

“We believe any strike action before the dispute resolution procedures have been followed would be unlawful,” a spokesman said after a company statement raised the prospect of taking the matter to the courts.

“Royal Mail will use all legal options at its disposal, including applying to the High Court for an injunction to prevent industrial action.” the company said.

The company added that it would contact the CWU to invoke the external mediation process under dispute resolution procedures agreed with the union in 2013. The mediation process could extend beyond Christmas, it said.

Royal Mail has about 142,000 UK employees and the CWU said on Tuesday that 73 percent of workers voted in the strike ballot, with 89 percent of its members voting for industrial action.

The dispute could threaten postal delays at Christmas if it continues.

“This is a watershed dispute that will determine not only our members’ pensions, jobs and pay, but also the future of the service,” CWU General Secretary Dave Ward said in a statement.

The union has said that Royal Mail’s move to replace its pension scheme would result in members losing, on average, up to a third of their future pensions.

Royal Mail was privatised four years ago and is one of the few big British companies to still have a defined-benefit pension scheme, which pays out a proportion of a member’s final salary determined by length of service.

Rising costs, falling investment returns and increased life expectancy have made it increasingly tough to fund such schemes.

Royal Mail wants to replace it with a modified defined-benefit scheme or a defined-contribution pension.