You can formally challenge an eviction notice by applying to the Residential Tenancies Board (RTB) for dispute resolution, explaining why you believe the notice is invalid or the termination is unlawful. Check the notice carefully for the required notice period, termination date, reason where required, signature and any other statutory requirements, and keep copies of all correspondence and tenancy records. Apply within the relevant RTB time limit, which can depend on the type of dispute, and do not ignore the notice while waiting. The RTB will decide the dispute based on the individual facts, so check the current guidance on rtb.ie or speak to a solicitor if the situation is urgent or complex.