The termination of employment without substantial grounds or fair procedure.
In Ireland, "Fair Procedure" is often more important than the reason for firing. Even if an employee was caught stealing, if you fired them without following a disciplinary process (warnings, right to representation), you will likely lose the case in the WRC.
It can be, if the redundancy was a "sham." If you let someone go for "redundancy" but then immediately hire someone else to do the exact same job, the WRC will view this as an Unfair Dismissal disguised as redundancy. Genuine redundancy requires the role to cease existing, not just the person.
Generally, an employee needs 12 months of continuous service to bring a claim for Unfair Dismissal under the Acts. Before this 12-month mark, it is easier to let staff go, but you must still be cautious of other claims (e.g., discrimination or dismissal for trade union activity) which do not require a service threshold.