City officials are not to be trusted when it comes to overseeing an upcoming referendum on how to finance and operate Regina's new sewage treatment plant, according to the group that pressed for a vote.

"We're very concerned," Jim Holmes, of Regina Water Watch, said Monday. "We can no longer trust [the city] to ensure a fair referendum."

Holmes said he has written to the province asking officials to provide "independent oversight" of the referendum.

The Water Watch group alleges City of Regina staff are in a conflict of interest by both overseeing the referendum and advocating for a result.

The city has launched an advertising campaign urging people to support a council decision to have the new sewage plant built and operated as a public-private partnership, or P3, arrangement.

Regina Water Watch wants the city to use a more traditional approach when it comes to the multi-million dollar project.