Mr Casson is being criticised for saying New Zealand should 'move on' from the terrorist attacks in Christchurch.
Mr Casson, a former police officer who later worked for Immigration New Zealand, posted on Facebook about the 15 March atrocity. He named the murder accused in the mosque attacks 20 times, and criticised the tightening of firearms legislation.
Hamilton mayor Andrew King told Morning Report: "Look I don't agree with anything councillor Casson has said and I don't endorse what he said.
"Councillor Casson will continue as a councillor but his views are inconsistent with what most New Zealanders and my council say. I think it's very insensitive. He's entitled to his opinions and that's his personal position.
"He has a track record for not supporting council's initiatives on working with ethnic communities and that's the position he takes ... Hamilton City Council has a close relationship with our ethnic and religious communities around cultural diversity but this member hasn't generally supported cultural diversity initiatives that council has put up."
Mr King wouldn't call Mr Casson's comments racist but did say they were unacceptable.
There didn't appear to be any way to take action against him, either.
"The initial assessment and opinion is that councillor Casson has not broken our code of conduct. It would appear there is no basis to discipline the member using the code of conduct. The member was giving his opinion as a democratically-elected member," Mr King said.
"Elected members are their own person they are not part of a party structure like central government, so each person has their own views.
"This be at the extreme end of the political spectrum and I believe the voters will have their chance to express their views at the ballot box this October."
He understood Mr Casson worked for Immigration New Zealand and expected his comments would "come up over the next few days or weeks between him and his employer".
Immigration NZ has responded to comments made by Mr Casson, stating: "INZ wishes to make it clear that it doesn't support the comments made by this employee."
RNZ's Morning Report has attempted to contact Mr Casson.
Fellow councillor Dave Macpherson says previous social media comments apparently by Mr Casson included a post in 2016 that calls for - quote - 'extreme violence to rid Europe' of refugees.
Cr Casson's council biography says he served for 26 years in the police and is a trained diplomatic protection officer.
He plans to run for mayor this year.
Mr King didn't go as far as calling Mr Casson's remarks hate speech, but said it concerned him that people could pick up on extreme views like Mr Casson's.
"Everything starts with a word. Words have power. And that is concerning."
Comments
I haven't heard of him before now but James R Casson is doing the ethical thing by not using ratepayers' money to favour certain groups of people over others, whereas Andrew King should be ousted from his job ASAP.