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FORMER Liberal MP John Alexander is copping it over a social media post critics say proves he is "disconnected" with the voters whose support he is trying to win back.

The former tennis great is fighting for the Sydney seat of Bennelong after resigning from representing the electorate in federal parliament over his citizenship status.

Now well and truly in campaign mode, Mr Alexander is doing all he can to convince voters he's better for the job than Labor's star candidate Kristine Keneally ahead of the December 16 by-election, but hit a snag with his latest social media stunt.

Last night on Twitter and Facebook, the parliamentary hopeful shared a picture of himself and four volunteers "chatting to local residents" on fixed line telephones.

The problem was, the phones weren't plugged in, and commenters noticed right away.

"Try plugging your phones in, they work better that way," one wrote on Facebook.

Another pointed out: "This is a visual metaphor for the LNP. Completely disconnected with the electorate and Australia."

Labor frontbencher Chris Bowen was among those pointing our the phone fail, taking to Twitter with some advice.

Mr Alexander's Facebook post has since been updated, assuring voters the phones they actually used to ring residents "were plugged in".

The campaign gaffe comes amid fears the Turnbull Government could lose its majority over the seat of Bennelong after Labor preselected former NSW Premier Kristine Keneally to run against Mr Alexander.

The latest poll reveals only one in five voters expect Malcolm Turnbull to hold onto government at the next election.

The latest Essential poll published on Tuesday puts Labor in a 54-46 two-party lead over the coalition.

Speaking at Sunday's campaign launch ahead of the Bennelong by-election, Opposition Leader Bill Shorten urged voters to send a message to Mr Turnbull when casting their votes.

"We know here that the time is nearly up for Turnbull and five years of incompetent, out-of-touch Liberal government in this nation," Mr Shorten said.

"Send a message about the incompetence and the division and the policy paralysis that is the trademark of the Turnbull government."

The December 16 by-election is the second brought on by the dual citizenship issue, but it's the only one Labor has a shot of winning. Deputy Prime Minister Barnaby Joyce faces a by-election in New England on December 2, but his margin is considered unassailable.

In Bennelong, Mr Alexander was also expected to comfortably retain Bennelong on a near 10 per cent margin until the former NSW premier was parachuted in.

A Galaxy Research poll published on Saturday showed the contest will be a tight race, with Labor boasting a 10 per cent swing on a primary vote basis, up to 39 per cent against the Liberal Party's 42 per cent.