Labor leader Bill Shorten has challenged Tony Abbott to take the fight against unions from the royal commission to parliament.

The opposition leader could face further grilling at the commission about his time as the Victorian and national secretary of the Australian Workers Union if he's recalled later this year.

Screenshot of Opposition Leader Bill Shorten giving evidence during the Royal Commission into Trade Union Governance and Corruption in Sydney. Credit:Kate Geraghty

Mr Shorten faced heat during two days of interrogation last week for declaring a $40,000 campaign donation made in 2007 only last Monday, and had his credibility as a witness questioned.

The Labor leader has declined to say whether he'll reappear and be cross-examined by his own lawyers, saying he's already answered 900 questions.