It's illegal because it threatens the viability and health of native populations of animals.
[1] https://www.cdc.gov/mosquitoes/mosquito-control/community/em...
The genetic modifications were classified as a biocontrol or pesticide, allowing them fall under the existing EUP process. I wonder whether showing that these sheep were being used to control a local crop pest would qualify them as a technical argument? :D
hahaha