"I note that the legislation that enabled the transfer of Pillar to Mercer provides a 10-year commitment to the Illawarra region and a two-year job guarantee for people who were transferred," he wrote.

"I ask that the NSW Government intervene and save these jobs in Wollongong."

Up to 25 staff at Coniston are set to go as Mercer reorganises to better serve a major client in Melbourne.

Read more: Mercer administration to cut jobs at Illawarra headquarters

Labor's Cr Brown said the city's economic development strategy, which aimed for 10,500 new jobs in ten years, required employers in knowledge services such as finance to sustain and grow their levels of investment in Wollongong

"The strategy is particularly targeting knowledge-based jobs, such as those at Mercer, to capitalise on the highly skilled talent pool Wollongong has in these areas," he said.

"Mercer makes a significant contribution to our community and I hope to see this continue well into the future."

Cr Brown said a recent study commissioned by the Advantage Wollongong lobby group concluded that as a location to set up a 150-person "knowledge centre" operation, Wollongong could offer savings of about 30 per cent compared with Sydney, Parramatta and Melbourne.

Mercer bought Pillar for $35 million in December 2016. Then treasurer Ms Berejiklian said the government was committed to keeping the Mercer jobs in the region.

"Pillar is a major employer in the Illawarra - that is why the government has secured the commitment of Mercer to maintain and ideally grow Pillar's operations in the region for at least 10 years," she said.

Assistant state branch secretary for the Community and Public Sector Union Troy Wright said the job losses were a betrayal of the terms of sale for Pillar.

"There was a promise made to us, our members and the people of the Illawarra that these jobs would stay," he said. "It goes to show that when organisations are privatised, a guarantee by government means nothing."

A NSW Government spokesperson had said the Government "will monitor the proposed changes and ensure obligations stipulated in the Act are honoured."