Malcolm Turnbull's son is encouraging voters to donate to Labor ahead of the Wentworth by-election.
The vacancy was created by the former prime minister's parliamentary resignation.
Alex Turnbull on Saturday re-tweeted Labor candidate Tim Murray's call for donations for the upcoming poll for the federal Sydney seat.
"Best bang for the buck you'll get in political donations in your life," the former prime minister's son, Alex Turnbull, said on Twitter.
The comments come after Alex Turnbull blamed the coal industry for his father's downfall.
In an interview with Fairfax Media on Monday, Alex Turnbull said supporters of the coal industry were exerting financial influence on the Liberal party, which worked against his father.
“It’s impossible to vote for the LNP in good conscience," he told the paper. "My father fought the stupid and the stupid won."
The Singapore-based fund manager said he knew Labor candidate for Wentworth Tim Murray as a friend, and party affiliation aside, said Mr Murray had his support.
In the interview with Fairfax Media, the younger Turnbull said: "[It's] hard to back a Labor guy but not Tim."
Before urging his followers to donate to Tim Murray, he retweeted an earlier message from Tim Murray in which he announced his official endorsement as a Labor candidate for Wentworth.
Social media users stunned
Alex Turnbull's position stunned users on social media, who probed him on whether he wanted to retract the statement.
Alex replied with a message saying: "Just the facts ma'am".
Another user said Alex had their vote if he planned on running in his father's seat of Wentworth, to which the younger Turnbull said he had no plans on entering the contest.
A number of social media users thanked Alex Turnbull for his "sage advice".
Others were criticised his position.
Alex Turnbull later clarified his position in an exchange with a social media user, saying he feels compelled to speak because of his loyalty to his country of birth, Australia.
Tight contest for Wentworth
Mr Turnbull, who first entered parliament in 2004, on Friday confirmed his resignation from the NSW seat of Wentworth in writing to Speaker Tony Smith.
Mr Smith said he was now considering possible dates for the Wentworth by-election, with ABC political analyst Antony Green anticipating a date of October 6.
The Wentworth by-election will be hotly contested both in terms of Liberal Party preselection and the poll itself.
Former Business Council of Australia executive director and same-sex marriage campaigner Andrew Bragg is emerging as the frontrunner to replace Mr Turnbull as the Liberal candidate.
Former Australian ambassador to Israel Dave Sharma and former prime minister Tony Abbott's sister Christine Forster are also in the running for preselection.
Business owner and City of Sydney councillor Angela Vithoulkas confirmed on Thursday she would stand as an independent.
Independent Kerryn Phelps, another City of Sydney councillor, is also considering a tilt.
- with AAP
