American metal foundries face an impending deadline to comply with tougher federal worker safety regulations intended to protect employees from a potentially fatal lung disease—silicosis.

Foundries and other manufacturers were given until June 23, 2018, to meet the requirements after the Occupational Safety and Health Administration released the rule in March 2016. A federal appeals court upheld the tougher OSHA requirements on Dec. 22.

Whether foundries, often using hundreds of tons of silica-based sand to cast metal parts, will...