Holcim New Zealand says a decline in local demand for cement means it will have to modify the design of a new factory near Oamaru, so it can export more.
The Environment Court last year declined an appeal against the proposed $300 million plant, which will produce about 900,000 tonnes of cement a year.
Holcim's capital projects manager, Ken Cowie, says cement sales fell by 20% last year because of the recession.
He says Holcim wants to modify the plant so that more of a cement product called clinker can be loaded onto trains for export from the Port of Timaru.
The changes fit within the consented boundaries and height restrictions, he says.
Holcim aims to have the plant built by 2014.