The accusate can have either the ending of the genitive (-n) and of the partitive (-a/-ta/-tta) or can have no endings. When a noun is the object of an imperative and of a passive verb, its form is the same as the nominative. Lauletaanpas is both imperative and passive, so the direct object can only be in the 'basic' form (the nominative). It's formally a nominative but its grammatical role is accusative
Last edited by Massimiliano B on 2014-12-27, 9:15, edited 1 time in total.
It might be worth not(h)ing that it's synonymous with "laulakaamme", though not as formal-sounding or whatever. I guess there's some type of a very subtle difference in the sense that "laulakaamme" would probably be used in more official contexts like at church or something. But most people would generally just say "lauletaan" in either situation unless they're talking to kids or are old, I think.