China’s smog-ridden Hebei province has asked steel, cement plants and utilities to adjust their production schedule between November and January as part of its battle against pollution, the Xinhua News Agency reported on Wednesday.

Companies ranging from petrochemical firms to metal producers will reduce output or shut down on heavy pollution days, Xinhua reported, citing the environmental watchdog of Hebei province.

There are no details on how the provincial government will implement the policy or the companies involved.

Hebei is China’s biggest steelmaking region, accounting for a quarter of the country’s steel output.

The province has already pledged to impose what it called “special emission restrictions” on local mills by setting up tough standards for sulphur dioxide and other pollutants，a policy document seen by Reuters showed.

Hebei is expecting weather conditions that will help trap pollutants and worsen its problems in winter, Xinhua said.