Lego says it will run out of bricks by Christmas.
Factories are running at maximum capactity but may not be able to make enough plastic bricks to keep up with demand from toy stores across Europe.
It's not clear which countries will be affected.
Lego has been popular for years but its business soared following the success of The Lego Movie.
The Danish company is now the world's largest toymaker by sales - after overtaking US Barbie-maker Mattel.
