Market factors, i.e. the availability of labour
Problems relating to the availability of labour, i.e. the competitive environment resulting from a shortage of qualified workers may be an acceptable reason for paying one employee a higher salary than another who is carrying out work of equal value. If a bonus is included in the pay for this reason, then this has to be done based on facts that have been clarified individually for each case, and not based on general presumption. In the case of litigation the employer has to be able to prove the shortage of qualified labour.
According to the European Court of Justice the following procedure has to be followed when examining proof provided by the employer: if a national court can determine precisely how large a portion of the difference in pay can be explained by market forces, then the difference in pay can be considered as having been objectively justified to that extent. If the portion of the difference in pay that was caused by market forces cannot be determined precisely, then the court has to assess whether or not the influence of the market forces on setting the level of pay was great enough for the employer to be considered as having presented an objective justification for the difference in pay partially or in its entirety. (Case Enderby C-127/92).