For blocks D, E. and F, the FCC has switched from the $40 million criteria to the under 1,500 employee category.
The FCC switched blocks D, E, and F due to the number of people employed there. 
mnli hypothesis: The FCC switched blocks D, E, and F due to the number of people employed there.  premise: For blocks D, E. and F, the FCC has switched from the $40 million criteria to the under 1,500 employee category.