Attorney-General Jarrod Bleijie is pulling out all stops to have a series of anti-government billboards across Brisbane taken down.

Fairfax Media has seen legal letters sent from the Department of Justice and Attorney-General to an outdoor advertising agency threatening it with prosecution should it not comply with requests to hand over correspondence between it and the company that booked the billboards, Not 4 Sale Limited.

CEPU Union's billborad on Brisbane Road, Bundamba, targeting the LNP State Government planned assets sales. Credit:Michelle Smith

Not 4 Sale was set up by the national Communications Electrical Plumbing Union (CEPU), which is affiliated with the Queensland-based Electrical Trades Union (ETU).

The ETU falls under the jurisdiction of the state Industrial Relations Act, which the Newman government amended to require unions to ballot members before spending more than $10,000 on such campaigns.