The way to say must/have to involves a negative conditional. There are three choices: the ば conditional, the と conditional, and ては for this grammar. These are followed by either いけない, ならない, orだめ.
So, for example, we can have, etc:
[Sentence] なければいけない。 = I must do [Sentence].
[Sentence] なくてはいけない。 = I must do [Sentence].
[Sentence]なくてはならない。 = I must do [Sentence].
[Sentence] ないとだめ。 = I must do [Sentence].
仕事に行かなければいけない。 must go to work.
(=If doesn't go to work, it's no good.)
部屋を掃除しなくてはならない。 I have to clean my room.
The difference between each ending is in formality: なくては is usually used in writing, and the other two are used in speech, but ないと is more casual than なければ. And the formality of the other endings is ならない > いけない > だめ, with だめ being most casual.
So your example sentence would be
襟付きのシャツも長いズボンも着用しなければなりません。