Authorities in one Pakistan province are turning to a controversial new tactic in the decades-long initiative to wipe out polio: prison.

Last month, the government in Sindh introduced a bill that would imprison parents for up to one month if they fail to get their children immunized against polio or eight other common diseases.

Experts at the World Health Organization and elsewhere worry the unusual strategy could further undermine trust in the polio vaccines, particularly in a country where many believe false conspiracies about them and where dozens of vaccinators have been shot and killed.

Adding to the problems faced by experts trying to persuade people of the vaccines’ safety: The oral vaccines themselves now cause most polio cases worldwide.