Haast Pass on the South Island's West Coast is scheduled to be closed overnight from Monday into Tuesday.
The road connects the West Coast and Otago regions, and will shut from 10pm Monday evening until 7am Tuesday, so work on the Ultra-Fast Broadband Southern Fibre Link project can be completed.
Waka Kotahi said if the weather does not allow the work to be done on Monday, the closure will be moved to Tuesday night instead.
It will affect all freight trips and drivers who use State Highway 6 between Otago and Westland - but emergency vehicles will be accommodated.
The highway will be closed near the Gates of Haast Bridge, but signs will advertise the closure at Haast, Makarora and south of Hokitika.