A growing number of Australians plan to boycott the census despite a "hand on heart'' promise their privacy won't be compromised.
Australia's 10 million households are legally required to give the bureau of statistics information about their homes, religion and income in the five-yearly snapshot tonight.
But politicians including independent senators Nick Xenophon and Jacqui Lambie say they'll risk a possible $A180-a-day (NZ$190) fine and withhold their names and addresses.
This is despite census head Duncan Young promising Australians that their data will be top secret.
"Hand on heart, the security set-up in order for people to submit their information - it's encrypted all the way through from their browsers into the ABS's internal environment,'' he told the Nine Network.
"Then we go through the process of separation. The information is isolated so people who can access names can't access the rest.''
The Australian Bureau of Statistics (ABS) has collected names and addresses since 1911 - but it will now keep data for four years instead of 18 months.
Mr Xenophon said he would introduce legislation that made giving your name optional in the future.
"Rather than be a snapshot of the nation, this census will morph into a mobile CCTV that follows every Australian,'' he said.
Greens senators Scott Ludlam and Sarah Hanson-Young also said they would leave their names and addresses off the census, while former New South Wales deputy privacy commissioner Anna Johnston said she would boycott it all together.
When asked by ABC radio how far she would take her potentially pricey protest, Ms Johnson said: "Let's just say I got an email from my accountant asking me the same question. I'm hoping it doesn't come to that. I'm hoping the ABS changes its decision."
However, Small Business Minister Michael McCormack earlier labelled the controversy "much ado about nothing'', saying people already handed over more information when they logged into Facebook or signed up to a supermarket loyalty card.
Census largest online event
Tuesday night's compulsory 61-question survey provides the ABS with a demographic snapshot and helps to determine the distribution of government funds.
More than two thirds of the population are expected to complete the 2016 census on smartphones, tablets and computers - after receiving their unique login codes and instructions in the post - which will make it the largest online event in the country's history.
Those in remote areas have been posted traditional paper forms, with 38,000 field officers doorknocking homes to help out the less tech savvy.
The Sydney Opera House is among 20 landmarks to be illuminated in green as a reminder to Australians to complete their forms, with a penalty of $A180 per day enforced after post-census letters and staff visits cease in mid-September.
