EXCLUSIVE

"The Amazing Race" winners Cody Nickson and Jessica Graf -- who previously met and became a couple on "Big Brother" -- may have led CBS to strike while the iron's hot ... and feature an all-'BB' cast for an upcoming season.

Sources close to production of 'Amazing Race' tell TMZ ... the show reached out to several past "Big Brother" houseguests and has locked down its list of competitors for the new season, which will begin filming soon.

We're told the all-"Big Brother" edition of 'Amazing Race' will feature at least one past 'BB' winner, but several other popular winners declined for family or career reasons. Still, we're told CBS is happy with the final cast ... and they're ready to race around the world.

Our sources say the idea for the "Big Brother"-themed season of 'Amazing Race' came from the success of season 30, which saw former 'BB' stars Cody and Jessica dominate.