While a California state senator, Thompson helped defeat legislation to halt the use of dogs in hunting of black bears and co-authored and voted for a bill (SB 28) to resume trophy hunting of cougars. SB 28 would have undone provisions of California Proposition 117 (the California Wildlife Protection Act of 1990) which had been approved by the voters in the statewide election held on June 5, 1990, that provided some protection for cougars. Thompson was the House sponsor of the Northern California Coastal Wild Heritage Wilderness Act, which was signed into law by President George W. Bush.