Learn Turkish: İşçiler madene girmemeli. - The workers must not enter the mine.

It starts with the verb root gir- (enter). We add the negative suffix -me, followed by the obligation suffix -meli (must/should). Because of vowel harmony with the i in gir-, both suffixes use the vowel e.

Why is there an -e at the end of madene?

The verb girmek (to enter) requires the dative case (-e or -a), which shows motion towards a destination. While in English you just "enter the mine", in Turkish you literally "enter to the mine". Therefore, maden (mine) becomes madene.

Since İşçiler is plural, shouldn't the verb be girmemeliler?

You can say girmemeliler, but it is not strictly required. In Turkish, when the subject of the sentence is explicitly plural and human (like İşçiler), the plural suffix on the verb is optional. Dropping it is very common and sounds completely natural.

Could girmemeli also translate to "don't have to enter"?