About 20 senior citizens have sent Queensland's government headquarters into lockdown with their protest against the Adani coal mine.
A spokeswoman at 1 William Street said the protesters entered the foyer with hidden banners about 11am on Monday.
Ten police were negotiating with the group, which was demanding a meeting with Environment Minister Leeanne Enoch.
They wanted assurances the government would prosecute Adani over an alleged breach of its pollution licence for releasing sludge into wetlands near the Great Barrier Reef in 2017.
"Adani has broken Queensland law and lied about how much toxic coal sludge they released," Galilee Blockade spokesman Ben Pennings said.
"With just 11 days left to prosecute, Adani has thus far got off scot-free. Labor must enforce our laws that Adani has clearly broken."
Liberal National Party Opposition Leader Deb Frecklington said the government should investigate whether any breach had been covered up, but said the project needed to proceed.
"We know that the environmental approvals are all in place and Adani needs to get going so that those jobs they've promised for regional Queensland start," she said.
"In relation to any prosecutions, that's up to the government to monitor and carry out as they should."