Water heater maker Rheem is set to close its Welshpool factory after more than four decades, slashing 100 manufacturing jobs.
The closure late next year - that will leave one of the world's sunniest places without a manufacturing industry for solar water heaters - will relocate up to 50 administration and sales jobs to NSW.
Rheem spokesman Gareth Jennings said the closure of the local factory was needed to ensure the company remained globally competitive.
Mr Jennings said Rheem's NSW facilities at Rydalmere and Liverpool and its Victorian operations at Moorabbin would have a $60 million expansion over the next two years to pick up WA's production, which specialises in solar heaters.
"The market for solar heaters globally and domestically has undergone many ups and downs lately and we can't justify a stand-alone factory in WA any more," he said.
Mr Jennings said Rheem had suffered under the high Australian dollar, which had helped reduce the price of imports from competitors and to undermine its exports.
Seven years of inconsistent State and Federal government policies on household incentive schemes and the Renewable Energy Target had also had an effect on the business, he said.
UnionsWA secretary Meredith Hammat said it was a tragedy for the workers as well as the manufacturing sector, which had steadily eroded over recent decades.