The Danish toymaker has put the major PR brief out to pitch as it plots a change in direction next year.
The account, currently held by The Red Consultancy, is believed to be worth about £175,000. The winning agency will be in charge of brand strategy.
Lego PR manager Melissa Wallace responded: 'We are pitching our business, but we are completely closed to other agencies. We want a change in strategy next year.'
Wallace said she did not expect to make a decision until the end of September at the earliest.
Red was brought in to promote Lego's educational benefits in September 2008. This was the first time for ten years that Lego had embarked on a campaign to strengthen its brand credentials.
Red's director of consumer brands Jo Slatem headed up the account, but in March this year she left to join Frank PR as a director.
A source at Red said it would not be working with Lego in 2010, owing to 'a change in PR strategy for the brand'. However, Red will be retained by Lego until the end of 2009.
Gloucestershire-based children's specialist Norton & Co, which handles PR for Lego's individual products, will not be affected by the review.
Lego has recently been in the news with reports Top Gear presenter James May is building a life-sized house entirely out of Lego bricks.
May has vowed to live in the house, which will have a working shower and toilet, for a weekend once it is finished.
It is being built in a vineyard in Surrey for the BBC series James May's Toy Stories. The house is expected to be built by the end of August.