Union ads attacking the Morrison government (Image: Facebook/Australian Council of Trade Unions)

Unions were a major force online during last month's election, pouring hundreds of thousands of dollars into digital advertising attacking the Coalition government and creating popular social media content.

Unions were among the biggest non-political parties spending on online advertising during the six-week campaign. More than a dozen spent at least $10,000 on advertising on Facebook, Instagram or YouTube over that time, with a handful spending more than $100,000.

The Australian Council of Trade Unions (ACTU) was the biggest spender, outlaying about $400,000 which was split evenly between Facebook and YouTube. It used a combination of video and image ads to attack Scott Morrison over low wage growth and high cost of living. These ads, focused on NSW, Victoria and Queensland, were seen more than 20 million times across both platforms during the last four weeks of the campaign.