ein Amt niederlegen
to resign
To voluntarily step down from an official position or office.
Der Minister hat nach dem Skandal sein Amt niedergelegt.
The minister resigned from his office after the scandal.

to lay down / resign
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to resign
To voluntarily step down from an official position or office.
Der Minister hat nach dem Skandal sein Amt niedergelegt.
The minister resigned from his office after the scandal.

'Niederlegen' (to lay down / resign) is a separable verb. In a main clause in the present tense or simple past, the prefix 'nieder' comes at the end of the sentence. In subordinate clauses and in the infinitive, the verb stays together.
Er legt den Stift auf dem Schreibtisch nieder.
He lays the pen down on the desk.
The verb is made up of 'nieder' (an old form meaning 'down') and 'legen' (to lay). The basic meaning 'to lay something down' can be found in all uses, whether it is about an object, an office, or work.
Der König legte seine Krone nieder.
The king laid down his crown.
The object of the verb reveals the exact meaning. 'Ein Amt niederlegen' means to resign. 'Die Arbeit niederlegen' means to go on strike. 'Einen Kranz niederlegen' is a ceremonial act.
Die Mitarbeiter drohten damit, die Arbeit niederzulegen.
The employees threatened to stop work.
The meaning 'to resign' is used almost exclusively with the object 'Amt' (office) or a specific position such as 'Mandat' (mandate/seat). The expression is 'ein Amt niederlegen' (to resign from an office).
Die Bürgermeisterin legte überraschend ihr Amt nieder.
The mayor unexpectedly resigned from her office.
In the meaning 'to record in writing', 'niederlegen' (to set down) is very formal and is used mainly in administrative or legal language. It implies that something is documented officially and permanently.
Die Bedingungen des Vertrags wurden schriftlich niedergelegt.
The terms of the contract were set down in writing.
To express that you lie down in order to sleep or rest, the reflexive form 'sich niederlegen' (to lie down) is used. This form is rather elevated or literary.
Nach einem anstrengenden Tag legte er sich früh nieder.
After a tiring day, he lay down early.
to hire / adjust / stop
'einstellen' and 'niederlegen' can both mean that work or an activity does not continue. 'einstellen' is more general: a company can stop or discontinue production, a service, or an activity. The reason does not have to be a protest. 'die Arbeit niederlegen' is used especially when people deliberately stop working in order to strike or protest. The words can be confused because both express an end to work. The important difference is: 'einstellen' is more about ending an activity; 'niederlegen' emphasizes a collective or deliberate work stoppage as a protest.

Die Beschäftigten legen die Arbeit nieder, weil sie bessere Löhne fordern.
The employees stop work because they are demanding better wages.
Die Firma stellt den Busdienst am Abend ein, weil zu wenige Fahrgäste mitfahren.
The company is discontinuing the bus service in the evening because too few passengers use it.