The findings, contained in September's Fairfax-Ipsos poll, show Labor has maintained the 53 per cent to 47 per cent lead in the two-party preferred vote it enjoyed in May, based on 2016 election preference flows.

If repeated on election day, there would be a 3.4 per cent swing away from the Turnbull government. If that movement was uniform, this would trigger a loss of 16 seats – which would comfortably hand power to the ALP given the government's slim one-seat majority.

But Labor strategists will be concerned at the big dip in voters' assessment of Mr Shorten's performance; approval of the Opposition Leader fell 6 percentage points since May, from 42 per cent to 36 per cent while his disapproval spiked from 47 per cent to 52 per cent, a statistically significant net 11 point shift.

Mr Turnbull's standing as preferred prime minister also rose 1 percentage point to 48 per cent, while Mr Shorten fell 4 percentage points to 31 per cent, widening the gap between the two men from 12 to 17 percentage points.

Offsetting these negative trends for Labor, Mr Turnbull's approval rating has fallen 3 percentage points since May to 42 per cent, and his disapproval has risen 3 percentage points to 47 per cent – placing the Prime Minister into net negative territory, according to voters' assessments.

The poll also found Scott Morrison enjoyed a 9 point lead over Chris Bowen as preferred treasurer, while 39 per cent of voters thought the Coalition was best-placed to manage the economy and 28 per cent thought Labor had the best economic policies.

These results suggest economic management could offer the Coalition a way back into the political contest ahead of the next election.

The findings come after three months of political trench warfare dominated by fights over electricity prices, energy and climate policy, ongoing debate about the same-sex marriage postal survey, and the citizenship fiasco that has engulfed three senior government MPs including Deputy Prime Minister Barnaby Joyce.

It also comes as the government has embarked on a so-called "kill Bill" strategy to damage the Opposition Leader. It has stepped up its personal attacks on Mr Shorten, while also repositioning Mr Turnbull as the underdog.

Coalition strategists will likely interpret the findings as proof the "kill Bill" tactic is starting to work and may also interpret the results as evidence the government's renewed focus on rising power prices, a key cost of living issue, is starting to cut through with voters.

At the same time, Mr Shorten has helped lead Labor's disruptive attacks on the government over the citizenship issue in parliamentary question time which, while effective tactically, may be a turn-off for voters.

Men, in particular, appear to strongly prefer Mr Turnbull as prime minister; he leads 51 to 31 per cent, whereas with women the lead is reduced to 46 to 32 per cent.

The primary vote of both the Coalition and Labor fell in the poll, to the benefit of the minor parties, with the Coalition's vote falling 2 percentage points to 35 per cent, Labor down 1 percentage point to 34 per cent, the Greens rising 1 point to 14 per cent and "others", including the Nick Xenophon Team and One Nation, rising 2 percentage points to 17 per cent, compared with May.

When voters were asked how they would allocate preferences – rather than relying on 2016 preference flows – the contest between the two major parties narrowed slightly, with Labor's lead reduced to 52 to 48 per cent.

Ahead of Parliament sitting on Monday, both Mr Turnbull and Mr Shorten both spent Sunday campaigning at events organised by supporters of a "yes" vote in the same-sex marriage postal survey.

In Mr Turnbull's first speech for the "yes" campaign since the High Court ruled the postal survey was valid, the Prime Minister told a "Liberals and Nationals for Yes" event "the right to marry is a conservative ideal as much as any other conservative principle" and that the law change would result in stronger families.

Mr Shorten told a separate rally in Sydney the campaign would be about one question only, "Do you support marriage equality in this country? ... when I support marriage equality, I do so because I believe in family values. I value all families – LGBTI Australians as well as all other families".

The nationwide poll of 1403 people was conducted from Wednesday to Saturday and has a margin of error of 2.6 per cent.