Learn Turkish: İşçiler yanlış tüneli kazmamalı. - The workers must not dig the wrong tunnel.

It comes from the verb root kaz (to dig). First, we add the negative suffix -ma to make it "not dig". Then, we add the obligation suffix -malı (must / should). Together, kaz-ma-malı means "must not dig" or "should not dig".

Why does tünel have an -i at the end?

The -i is the specific direct object suffix (accusative case). Because the workers must not dig a specific tunnel (the wrong one), we must add -i to tünel to make it tüneli.

Since the subject İşçiler (The workers) is plural, why isn't the verb plural (kazmamalılar)?

In Turkish, when the subject is explicitly stated in the sentence and refers to plural humans (like işçiler), adding the plural suffix -lar to the verb is optional. Saying kazmamalı instead of kazmamalılar is completely correct and sounds very natural.

How does the word işçiler break down?

The root is iş, which means "work" or "job". The suffix -çi is a profession suffix (similar to "-er" in English), making işçi (worker). Finally, -ler is the plural suffix, giving us işçiler (workers).