Royal Mail Plc offered to take a dispute over pay and working practices to arbitration as further strikes involving 115,000 workers loom.

The UK postal firm has written to the Communication Workers Union to propose talks at the state-backed Advisory, Conciliation and Arbitration Service, it said in a statement Thursday.

At the same time, Royal Mail said it will review or serve notice on historic agreements and policies it says are being used to “frustrate transformation.” The CWU said on Twitter that those comments amount to an “all-out attack” on unionization, without making reference to the offer of arbitration.

Royal Mail staff plan to walk out on Sept. 30 and Oct. 1 after canceling action due last week after the death of Queen Elizabeth II. Previous strikes on Aug. 26 and 31 led to several days of delays in deliveries of some postal items.

Labor strife at Royal Mail has deepened as unions resist management plans to shake up operations after the Covid crisis accelerated a slump in letter volumes while boosting the parcels business amid a shift to online shopping. With those trends persisting, the firm wants to shift more deliveries to the afternoon and evening to better meet next-day demand.

Rail Meeting

Workers are also seeking pay rises in line with soaring inflation, joining staff in industries across Britain in staging walkouts amid a cost-of-living crisis.

The National Union of Rail, Maritime and Transport Workers said separately that more than 40,000 members will strike on Saturday, Oct. 8, at 15 train operating companies and track and stations owner Network Rail Ltd., in addition to a planned walkout on Oct. 1.

While calling the action, RMT General Secretary Mick Lynch said that new UK Transport Secretary Anne-Marie Trevelyan had met with the union, and though no new pay offer has been made, the step suggest a “more positive approach.”