An Iowa regulatory board won’t let Alliant Energy charge customers who decline to have smart meters used to track how much electricity they use.

The Iowa Utility Board voted Wednesday to reject Alliant’s request to charge $15 a month to customers who opt out of the smart meter program. The board told Alliant to file a revised rate request that lets allows customers opt out without facing a fee. The board says Alliant already charges customers for meter reading in its current rates.

The board didn’t bar Alliant from seeking a future charge in a broader rate case.

Alliant says its smart meter system uses two-way wireless communication to retrieve meter data and funnel it through a secure and proprietary network.