While I don’t doubt it would be ruled unconstitutional in the US, election day media bans are enforced in many functioning democracies (including Iceland, Israel and the UK). However, it can be debated how effective these bans are in the wake of social media. Also repercussion for braking this ban is also quite often minimal (two parties were found guilty of violating it in the last Icelandic parliamentary election, and no punishment was given).