NZ Steel has confirmed it's proposing to cut up to 200 jobs and change some products as it looks to cut costs.
The company employs 1400 people and has been reviewing its operations for several weeks.
"New Zealand Steel will continue to manufacture New Zealand's iconic COLORSTEEL building products," chief executive Gretta Stephens told 1 NEWS.
"However, we are proposing to change the mix of products and continue our focus on reducing costs to become a leaner and more resilient business that is 'fit for purpose, fit for market'."
Stephens says the business is being reshaped for a "sustainable future".
"New Zealand Steel has been battling local and international headwinds for several years and hasn't delivered the required investment returns," she says.
"Unfavourable public policy in relation to carbon, energy costs and trade remedies have compounded the financial pressures and the business can no longer continue in its current operating model."
No stone was left unturned in the review, Stephens says.
"The review carefully considered all options available to us, with varying results for our business, including operating costs, product lines, people and revenue."
Briefings will now be held with staff, customers and suppliers.
NZ Steel has been producing at Glenbrook for five decades.