The invitation is among a number of items that are up for auction from the 'I Wanna Go' singer's wedding, according to TMZ.
Crafted from ivory lace and covered with Swarovski crystals, the wedding invite is addressed to Federline's grandparents Earl and Betty Story. It is being auctioned by Earl Story in the wake of his wife's death.
A rose petal holder, a napkin ring and an invitation to Spears's baby shower for her son Sean Preston are up for sale as well.
Spears and Federline finalised their divorce in 2007.
In mid-June, it was rumoured that Spears is secretly engaged to her ex-manager Jason Trawick, though the singer's UK publicist denied the reports.
Earlier this year, Spears hinted that she hopes to marry Trawick sometime in the future, stating that she feels very comfortable with him.
Watch Britney Spears's music video for 'I Wanna Go' below: