Freedom of the press must not be obstructed.

Literal

Press [possessive-の] freedom [topic-は] obstructed-[passive-されて] [must-not-はならない]

~てはならない is the formal 'must not' — a stronger, more principled prohibition than ~てはいけない. 阻害される is the passive of 阻害する (to obstruct). The sentence reads like a constitutional principle.