can I treat an employee differently after they asked about salary

No detriment following a question about pay is permitted

No, treating an employee differently — that is: less favourably — because they asked about pay is not permitted. The right to ask about compensation is explicitly not a discretionary favour from the employer; it is a right that the employee may exercise without facing any adverse consequences. This means that a less favourable assessment, the cancellation of a promotion, being skipped for a bonus, or a cold atmosphere that clearly arises as a reaction to that question cannot be justified if it is directly linked to that question.

This applies not only to the employee who asks themselves, but also to someone who helps or supports a colleague in doing so — a representative, a confidant, or someone who thinks along internally on such a request. That person also enjoys the same protection. For the employer, this means in particular that handling such a request must be kept separate from the rest of the assessment: a request for information is a separate process, with its own approach, and not something that runs alongside the performance review in that same month. How such a request must be answered precisely is described at an employee asks about average remuneration — what must I provide, and who may ask at all which employees may submit an information request about compensation.

Where this right comes from

This follows from Article 7 of Directive (EU) 2023/970, which establishes the right to information about compensation and protects workers against detriment as a result of exercising that right. The Equal Treatment of Men and Women Act additionally provides the broader framework within which unequal treatment on the basis of sex — including detriment following a question about compensation — has long been prohibited. Both sources point in the same direction: asking the question itself must never be the reason for an adverse decision.