The couple, whose Chaotic reality TV series is currently airing on digital channel E4, don't want the video made public.
According to Us Weekly, a member of the couple's entourage "has threatened to release raunchy footage of the two taken before Spears looked pregnant".
The video was allegedly copied from a tape in the Spears/Federline collection.
But don't expect the "hot sex" Spears always brags about.
A copy of the original tape viewed by the couple's lawyers "elicited laughter and disgust", according to reports.
Spears, 23, gave birth to a baby boy last month.
The singer married dancer Federline, 27, in September 2004 after a six month romance.
