Ryanair Holdings Plc has threatened to freeze benefits for pilots in Dublin and move aircraft to other Irish airports if staff go on strike. The discount carrier will scrap promotions, halt transfer requests and cut back recently-granted spending allowances of up to 16,000 euros ($18,900) per pilot, Chief People Officer Eddie Wilson wrote in a letter to staff seen by Bloomberg News. The company may “in due course” look at moving aircraft away from the Irish capital to bases that have accepted a pay increase and new contract terms. A spokesman for Ryanair declined to comment on an internal communication between management and staff. Ryanair is battling deteriorating relations with crew after a pilot shortage in September forced it to cancel flights for 700,000 customers. Italian pilots on Wednesday said they would take strike action on Dec. 15 for four hours. Employees in another six countries are voting on similar moves, with the results being tallied in Ireland in the coming days. If crew support a union-backed walkout, “then we intend to meet this head on,” Wilson wrote. He added that Dublin pilots “are being misled by Aer Lingus pilots into possible industrial action”—a reference to the fact that the Irish Air Line Pilots’ Association, IALPA, is dominated by staff from its Irish competitor. The letter comes after IALPA wrote to Ryanair Chief Executive Officer Michael O’Leary last week warning of action if the carrier refused to engage in negotiations with an ad hoc pan-European group. Ryanair’s three other Irish bases have now accepted pay increases of as much as 22,000 euros, Wilson said.