LONDON (AP) — U.K. politicians who want Britain to leave the European Union are fighting back after President Barack Obama sided with those who want the country to stay in the 28-nation bloc.

Justice Secretary Michael Gove led the charge Monday, arguing the U.K. will face a migration "free-for-all" if it votes to remain in the EU in the June 23 referendum. The comment comes after Obama told Britons they would be at the "back of the queue" for a trade deal after an "out" vote.

Gove told the BBC "nobody knows" how long a trade deal would take.

London Mayor Boris Johnson, a supporter of the exit campaign, also spoke after being condemned for his personal attacks on Obama. Johnson said those favoring EU membership should not "crow too soon."