A warning can feel both personal and urgent. The best first action is usually not a long rebuttal written the same evening.
Break the document into claims
For each allegation, identify the date, expected duty, described conduct and source. Does the letter state what should have happened instead? Does it refer to a policy or instruction you can locate? Separate disagreement with the facts from disagreement with the interpretation.
Preserve the warning, envelope, attachments and relevant messages. Write your recollection while it is fresh, but label it as your own note. Avoid contacting colleagues for statements in a way that could place pressure on them.
Decide the purpose of a response
A response might correct a date, supply an omitted document, deny a specific account, or request that your statement be placed with the personnel record. It should not become a catalogue of every difficulty in the employment relationship.
Ask for the applicable internal procedure and consider support from a works council or trade union. A qualified employment lawyer can advise on legal consequences and the appropriate formal response; practical consultation does not replace that assessment.
Watch the wider context
If the warning arrives with a termination, proposed agreement or another binding deadline, seek legal advice promptly. In Germany, a dismissal challenge commonly has a three-week filing period. Do not let work on a perfect internal letter consume the time needed for legal action.
A careful response is anchored to sources and a clear purpose. Its value comes from precision, not volume or indignation.