Labor leader Bill Shorten has responded to Malcolm Turnbull's vow to fight an election on trade union reform, taking to Twitter to declare, "Bring it on".

After the release of the trade union royal commission's final report on Wednesday, Mr Turnbull flagged major reforms to union governance and said he would make it an election issue if the Senate blocked new laws.

On Thursday Mr Shorten, who is on leave and did not front the media on Wednesday, tweeted: "If Mr Turnbull and his Liberals want to fight an election on industrial relations, bring it on. We won on WorkChoices & we'll win again."