Family First senator Bob Day is set to return to the Senate chamber to vote for the government's industrial relations legislation despite announcing his resignation from Parliament.

The South Australian announced his resignation last week after his housing construction empire went into liquidation, but is yet to hand his formal resignation to Senate President Stephen Parry.

But in a statement to Fairfax Media, Senator Day noted he had only expressed an "intention" to resign and left the door open for a return to Parliament when it resumes next month.

The delay in choosing his replacement will likely mean Senator Day returns to Parliament in November to vote for the re-establishment of the controversial Australian Building and Construction Commission and creation of a new body to oversee trade unions, legislation he has long publicly backed.