Charlton to visit north Essex.
A last minute winner from Callum Harriott in the Second Round against Altrincham gave the U's a 3-2 victory and a place in the draw on Monday evening.
And the draw sees the U's face the parent club of the mercurial winger.
The tie will be played on the weekend of January 9th, with full details to be announced in due course on the club's official website and social media channels.
With the U's facing Charlton, the scheduled match against Fleetwood Town on January 9th has been postponed and will be rearranged.