relative pronouns - "To ensure" vs. "To ensure that" + subject + predicate

Is any of these two sentences incorrect:

-(without that): "To ensure the voters are not influenced by mass-media, the campaign will end 7 days before the elections take place."

-(with that): "To ensure that the voters are not influenced by mass-media, the campaign will end 7 days before the elections take place."

Is the presence of that mandatory?

Answer

I agree with both the previous commentators. WS2 is correct in saying that the relative pronoun here 'that' is frequently elided. I share Hot Licks's view that inclusion of 'that' is stylistically preferable.