That's the scoop according to Matt Hughes:
Just found out a few days ago that Robbie Lawler will fight Jake Shields on the Strikeforce card on June 6th, in St. Louis. It’s great to have Robbie fight that close to home. We were worried that he would fight in the month of May close to my fight, so it actually turns out to be a pretty good schedule. As always, Robbie’s a performer and puts on fights that people want to see.
The bout has been announced for May in Seattle but this appears to have changed. When contacted by MMANews.com, Strikeforce officials did not have a date set for the bout.