The expression "automatically unfair dismissal" is not a term of art and does not appear anywhere in the Employment Rights Act 1996. It is a colloquial expression used to describe dismissals for certain statutorily specified reasons. If a dismissal is for one of those reasons a tribunal must find that the dismissal was unfair. The reasons are mainly those set out in ERA 1996 ss.99 -105 and TULR(C)A 1992 s.152,153 and 238A, the self explanatory headings of which are set out below. New laws giving new rights to employees may themselves provide that dismissal of an employee for exercising those rights will be automatically unfair (for example the Part-time Workers (Prevention of Less Favourable Treatment) Regulations 2000, SI 2000/1551, reg 7 and see also notes at Unfair dismissal/automatically unfair dismissals/assertion of statutory rights ).

The expression "automatically unfair dismissal" is also sometimes used more loosely to refer to dismissals in circumstances which are unlawful under the sex, race or disability discrimination legislation. However that use of the expression can be misleading as it tends to play down the role of the tribunal in deciding whether the circumstances of the dismissal were unlawful.

If a dismissal is automatically unfair, statute usually removes the normal need for the employee to have completed a minimum period of employment (ERA 1996 s.108) or to be below a specified age limit (ERA 1996 s.109) to qualify for unfair dismissal. If dismissal is automatically unfair a tribunal does of course still have discretion as to the amount of compensation to award, subject in some cases to a statutory minimum - see Unfair dismissal/basic award/minimum in certain cases .

The detail of the reasons which make a resulting dismissal automatically unfair is set out in ERA 1996 s.105 (as regularly updated) and Trade Union and Labour Relations (Consolidation) Act 1992 ss.152, 153 and 238A - see also the list in this program at Unfair dismissal/automatically unfair dismissals .