Next month’s state opening of parliament, one of the set-piece events in the UK political calendar, could face serious disruption after House of Commons security staff announced they would strike to coincide with it. The Public and Commercial Services Union (PCS), which represents 250 parliamentary security staff who announced initial plans for a strike earlier this month, said any delays or queues on 7 November, when King Charles will deliver his first speech to parliament as monarch, would be the fault of the management. Parliamentary authorities plan to use extra police officers to cover the work of the security staff for the state opening, when large contingents of MPs, peers and other dignitaries descend on Westminster. However, a PCS source said it remained possible there could be “serious delays” in people getting into the parliamentary estate, pointing to a strike by PCS security staff at courts last month, when about 30 closed despite efforts to mitigate the impact. Unless there is a resolution, security staff will stop work from 7pm on 6 November until 7pm on 7 November, as well as for 24 hours from the evening of 31 October. Any significant queues or delays to the state opening would be embarrassing for parliamentary staff. At the event, which starts a new session of parliament, the monarch delivers a speech in the House of Lords setting out the government’s legislative programme. An official called Black Rod is sent to the Commons to bring MPs to the Lords, with the door to the chamber shut in his or her face in a symbolic act of the independence of the lower chamber. The PCS, a trade union for civil servants and public sector contractors, announced the strike after security staff in parliament voted for industrial action, with 95% in favour on a 79% turnout. The strike is in response to guards being asked to work extra night shifts to cover for a lack of staff, amid wider discontent about their treatment. A source in the parliamentary estate management said it was confident the extra police officers would be able to carry out the work and avoid any queueing. But Mark Serwotka, the PCS general secretary, said any disruption “would come as a direct result of the poor treatment that has been doled out to our members by their managers”. He said: “Our members who work as security guards in the House of Commons understand the true value of their work. It is a pity that management clearly don’t. “Until management suspend the new roster, give our members a proper work/life balance and recruit sufficient staff to cover all vacancies, our members intend to do everything within their power to demonstrate the importance of their work by maximising disruptions.”