Both will square off in a public debate to be presided over by Auckland SPCA executive director Bob Kerridge.
The September 19 showdown will form the centrepiece of the 25th New Zealand Companion Animal Conference, to be held in Rotorua.
The Morgan Foundation blamed cats for causing harm to 33 endangered native bird species and the extinction of a further nine.
It called for pet cats to be fitted with bells, kept inside at all times and not replaced after they die, and for homeless cats to be either homed or eradicated.
Mr Avanzino, a former president of the San Francisco SPCA, rubbished this as "illogical".
"There are people probably in every country who think that's the right approach, but I don't know any country that has an ideology that pushes that agenda," he said from California.
"Here in America, we've gone from killing 24 million cats and dogs each year, to less than three million."
Many of the arguments targeting cats proved to be unfounded, unreal and inappropriate, he said.
"I don't know a lot about New Zealand, so I confess my ignorance here, but in the US, the primary threat to indigenous species walks on two legs, not four."
Dr Morgan was overseas and could not be reached, but Morgan Foundation economist Geoff Simmons stood by the hardline cat campaign.
"We don't see it is extreme at all - all we are asking for is cats to be managed just like we do dogs already," he said.
"Most of the polls and surveying we've done shows people agree with that."
Many Kiwis believed the foundation wanted all cats to be killed, but this was false, he said.
"We don't have any problem with responsible pet owners."
Mr Simmons said it was normal in the US to keep cats inside, and Australia had looked at cat curfews. Homeless cats were a different issue: the foundation opposed the SPCA's trap-neuter-release policy and considered the animals not stray but "feral".
"They're wild, they're not owned, and having colonies of them roaming the countryside in a country where we have one of the highest levels of endangered bird species in the world ... it's just environmental vandalism."
Other international guests for the debate will include Jon Cicirelli, San Jose's director of city animal care and services, and Joy Verrinder, of the Animal Welfare League in Queensland.
For more information on the conference, visit www.nzcac.org.nz