The federal government will spend a further $15 million advertising the national broadband network between now and next June - ahead of the next election.

Government agencies have already spent $29 million advertising the project since 2010, according to the Department of Finance, while NBN Co itself spent $8 million on advertising in 2011-12.

"The NBN is the biggest infrastructure project in Australia's history" ... Stephen Conroy. Credit:Michele Mossop

The government claims a joint parliamentary committee highlighted the need for more advertising. But committee chairman Rob Oakeshott said it did not officially recommend more advertising and the upcoming campaign would have to be a ''much better standard of advertising than we have seen to date'' to justify the $14.7 million price tag.

The department's last NBN campaign was ''bland, blancmange and shameless … that in the eyes of many was a waste of money'', Mr Oakeshott said.