INDIANAPOLIS — An Indiana proposal that would allow “baby boxes” in public places such as fire stations to give mothers in crisis a way to anonymously surrender their children faces a backlash from advocates of safe havens across the country who see it as going too far.

At least three safe haven groups have issued statements opposing the proposal, which would add the boxes to an existing Indiana law that allows a newborn to be surrendered without prosecution so long as the child hasn’t been harmed. One group, Baby Safe Haven-New England, has called the idea a “fiasco” and has compared it to a 2008 safe haven law in Nebraska that resulted in children as old as 17 being abandoned at hospitals before lawmakers changed the law.

Michael Morrisey, co-founder of the New England group, has taken to Indiana radio stations and social media to oppose the baby box plan. He said Massachusetts considered baby boxes more than a decade ago but determined they wouldn’t be effective because their electronics can fail and because it would be cost-prohibitive to retrofit existing buildings to include the boxes.

Monica Kelsey, a Woodburn, Indiana, firefighter and medic who is working with Republican state Rep. Casey Cox on the box proposal, said she expected to encounter disagreements over strategies for preventing abandonments but wants the focus to remain on saving children’s lives.

She stressed that installing the boxes would be voluntary and that they should be considered a last resort for women who can’t face relinquishing their babies in person.

The boxes, which would be about 2 feet long and equipped with heating or cooling pads, would include a toll-free number staffed 24 hours a day by a counselor who would first ask the caller to surrender the baby to a person. They also would be equipped with sensors that would set off alarms when the box is opened and again when a weight is detected inside. They also would include a silent alarm that mothers could activate themselves by pushing a button.

The state health department would develop regulations for the boxes, and sites that install them, such as hospitals, police and fire stations and churches, would register with the state.

Cox said Friday that he has spoken with several safe haven advocates about their concerns and hopes to draw on their expertise to ensure the bill strengthens the state’s existing law.