Learn Turkish: Açığa alınan memurlar yeni kararname üzerine şikâyet etti. - The officers who were suspended complained upon the new decree.

Here, üzerine acts as a postposition meaning 'upon' or 'as a result of'. For this abstract meaning of immediate sequence or response, it usually attaches directly to the bare noun or noun phrase (yeni kararname). If you used the genitive structure (kararnamenin üzerine), it would sound more like physical space, meaning 'on top of the decree'.

What does açığa literally mean here, and how does it translate to 'suspended'?

Açığa comes from açık (open) plus the dative suffix -a (to), literally meaning 'to the open'. The passive phrase açığa alınmak (literally 'to be taken to the open') is a fixed Turkish idiom used specifically for being temporarily removed or suspended from a job or official duty.

How does the suffix -an work in the word alınan?

The suffix -an is a subject participle (often translated as 'who', 'which', or 'that'). It attaches to the passive verb alınmak (to be taken) to turn the entire verb phrase into an adjective. Together, açığa alınan means 'who were suspended' and directly modifies the noun memurlar (officers).

Since memurlar (officers) is plural, why is the verb şikâyet etti singular instead of ettiler?