Former deputy prime minister Barnaby Joyce has dared the Labor Party and the union movement to bring a legal challenge against any of the decisions he oversaw before he was thrown out of Parliament by the High Court.

More than 100 Turnbull government decisions could be vulnerable to legal challenge as a result of Barnaby Joyce and Fiona Nash's dual citizenship status, with lawyers engaged by the Labor Party concluding there is a high likelihood the work the pair has done over the past year will end up before the courts.

The Australian Council of Trade Unions has also commissioned legal advice about the validity of a parliamentary vote on penalty rates.

The question mark over decisions that were made while Mr Joyce and Ms Nash were in Parliament adds to the sense of chaos Labor is trying to create around the Turnbull government following the High Court's decision on Friday which disqualified five MPs - Mr Joyce, Ms Nash, Malcolm Roberts, Larissa Waters and Scott Ludlam - from Parliament because they held dual citizenship.