Organic and free-range chickens have been thrown into lockdown. Egg-laying hens that normally have access to the outdoors can no longer roam as freely or feel the sun on their beaks as some US and European farmers temporarily keep flocks inside during lethal outbreaks of bird flu, according to egg producers and industry representatives.

The switch comes as a surprise to shoppers already shelling out more money for eggs due to cullings of infected flocks. Consumers pay extra for speciality eggs, thinking they come from hens that can venture out of barns.

US watchdogs say retailers and egg companies must do a better job informing customers that hens are kept inside, as shoppers track their spending amid record global food inflation.

Keeping birds inside is safest for now, according to...