Labor says the government should ban foreign donations to the campaigns for and against same-sex marriage.
New enrolments and changes to the electoral roll ahead of the historic survey close at midnight on Thursday.
Labor leader Bill Shorten attended an event urging a "yes" vote on Thursday, and said the government should ban foreign donations and ensure donations over $1000 be disclosed in "real time".
"I think the Turnbull government should rule out foreign donations coming into this marriage equality issue. I think it's wrong," Mr Shorten told reporters in Melbourne.
A parliamentary committee report released in March called for a ban on donations from foreign citizens and foreign entities to political parties, associated entities and third parties, but it has not yet been acted upon.
Labor has also been arguing for tighter controls on campaign material, and urged the public to report any offensive pamphlets and posters to a parliamentary inquiry looking into the handling of the postal survey.
A Chinese language pamphlet doing the rounds of Sydney and Melbourne urges a "no" vote, arguing: "Homosexuality is a curse of death in terminating the family line."
Malcolm Turnbull urged all Australians to update their electoral roll details.
The prime minister reiterated his support for a "yes" vote, and believed a private member's bill would "sail through the parliament" if the survey came back with a "yes" majority.
An Essential poll published on Tuesday found 57 per cent of voters favoured changing marriage laws, while 32 per cent were opposed.
However, the voluntary postal survey - which was put in place after Labor rejected a compulsory plebiscite model - was only favoured by 39 per cent, with 49 per cent against.
Voters can go online at www.aec.gov.au to enrol, or pick up a form at a post office or AEC office.