Niantic Labs, the company behind Pokemon Go, has confirmed that it will be temporarily closing gyms in the game from the 19 June.
In a statement by the company, the developers of the smash hit AR game stated:

"Gyms will temporarily close starting Monday, June 19. Any Pokémon you've assigned to Gyms will be returned to you at that time."

The move, the developers state, is ahead of a new update that was announced earlier in June.

"To kick things off, we will be hosting the Solstice Event starting on June 13, 2017. This in-game event will feature Fire-type and Ice-type Pokémon, huge XP bonuses for throwing Poké Balls accurately, and discounted Lucky Eggs in the in-game shop. Soon thereafter, you can look forward to a new update focused on collaborative group gameplay features that will get you playing Pokémon GO in fun new ways," explained Niantic Labs on the 8 June. "In preparation for these exciting features, we’ll be temporarily disabling Gyms for a short period of time."

The company has not said how long the Gyms will be offline for, or what the new features will be when they return, although it’s rumored the company wants to overhaul gyms to help fight cheating. It might also introduce raids, allowing players to team up or play against one another in the gyms.

A spokesperson for Niantic confirmed on Reddit that the move is so Trainers can collect their Defender bonus points:

"As we get ready to update Pokémon GO, we want to ensure that Trainers have a sufficient heads up that Gyms will soon be disabled so that they can collect their Defender bonus. We will provide updates on our social channels in advance of Gyms closing in-game."

We will keep you posted.