Yesterday Ms Simcock said they had not heard yet what had happened at the meeting but news of the protest had "been communicated".
Ms Simcock described the meeting as an "industry roundtable" with groups involved in the Thai fishing industry.
She said the meeting was about looking at sustainability as well as traceability and labour issues, and new ways to solve these problems.
Mars spokeswoman Vicki Hamilton said Thai Union had signed its supplier code of conduct and the Mars Fisheries code of conduct, and were audited against it.
"We have been consulted for SeaChange, the Thai Union sustainability strategy, and believe that the company is putting strict measures in place to drive responsible sourcing, marine conservation, safe and legal labour and caring for communities," she said.
"Forced labour and human rights abuses in general are very serious issues that cannot be solved overnight but need thorough understanding of the supply chains to develop an efficient and effective plan to eradicate.
"Thailand is of strategic importance to Mars for this region. We believe that as a global and local business we have a responsibility to contribute to the change the Thai fishing industry needs to make to become a reliable and sustainable supply chain. As such, it is vital that we engage with, rather than abandon, the industry - working with others, including Thai Union, to improve conditions and to stamp out any human rights abuses."
She said Mars was a member of Aim-Progress, an organisation that helps businesses conduct human rights due diligence reviews of their supply chains and ensure implementation of the UN Guiding Principles for business and human rights.
"The Mars Whanganui team are grateful for the support provided by the community last week, including the police and suppliers, during the presence of Greenpeace."