Learn Finnish: Kaikkien työntekijöiden on noudatettava sääntöjä.

Both express obligation, but on noudatettava uses the 'on' + passive present participle structure (verbs ending in -tava or -tävä). This translates closer to 'is to be followed'. It is more formal than 'täytyy' and is very common in official rules, workplace instructions, and written laws.

Why is the subject kaikkien työntekijöiden in the genitive plural instead of the nominative?

In Finnish necessity structures (just like with täytyy or pitää), the subject who has the obligation must be in the genitive case. Since 'all employees' is plural, both words take the genitive plural ending -en / -den.

If 'all employees' is plural, why is the verb on in the singular form rather than ovat?

In necessity structures, the auxiliary verb (like on, täytyy, or pitää) is permanently frozen in the third-person singular. Because the subject is in the genitive case, it doesn't grammatically 'own' or control the verb like a normal nominative subject would.

Why is the object sääntöjä in the partitive plural here?

Normally, objects in necessity sentences follow special casing rules (often looking like the nominative). However, the verb noudattaa (to follow / to comply with) is a partitive verb. This means it strongly requires its object to always be in the partitive case, which overrides all other object rules.