At least in the U.S., it's a complete non-issue for an output power that can easily cover the size of a wedding reception as long as you're not using a wide-band transceiver.

You'll want to be "kind" to the extant spectrum and do a responsible frequency sweep to select the "quietest band" prior to broadcasting. And you'll only want to broadcast during the event itself.

The FCC has better things to do than to try and track down an ephemeral milliwatt infringer.