The veteran French actress, who is a longtime campaigner on animal welfare issues, recently penned an open letter to Australia's environment minister Greg Hunt criticising plans to rid the country of two million feral felines.
"This animal genocide is inhumane and ridiculous," she wrote. "In addition to being cruel, killing these cats is absolutely useless since the rest of them will keep breeding."
Morrissey also condemned the planned cull, calling the Australian government a "committee of sheep-farmers who have zero concerns about animal welfare or animal respect".
The comments have now prompted a response from the government's Threatened Species Commissioner Gregory Andrews, who has written to both stars to explain the situation.
In the letters, which he has published online, the politician tells the stars the cull is necessary to prevent hordes of feral cats wiping out indigenous species which are becoming extinct.
"I would like to commend you for your commitment to, and advocacy for, animals and their welfare," he writes. "We have lost 29 unique Australian mammal species over the last 200 years... Much of this animal species loss is due to very high levels of predation by feral cats...
"We don't want to lose any more species... It is with this sentiment in mind that the Australian government has taken a stance on feral cats; for the protection of our native species that belong here."
He adds to Guardian Australia, "It's an unusual situation. I'm glad people like them care about animal welfare and I care deeply about animal welfare too.
"The threat to our wildlife are clear and feral cats are top of the list. We don't hate cats but we don't have a choice. We will do this as humanely as possible and we will reduce the net suffering of animals in Australia...
"I sleep very well at night knowing what we are doing. Australians support this. Brigitte Bardot and Morrissey have a lack of understanding of Australia and what we are losing. They aren't Australians, they aren't experiencing the extinction crisis we have here."