SYDNEY: Australian Prime Minister Malcolm Turnbull, whose leadership has been questioned after a series of political setbacks, secured a much-needed legislative victory on Tuesday with the passage of one of the two bills he used to trigger an election this year.

Australia's Senate, which the government does not control, passed a labor bill in an early morning sitting that will see greater oversight of trade unions and employer organizations.

Turnbull has seen his poll numbers slide to their lowest levels since he assumed the leadership in September 2015, and his future as prime minister has been questioned by political commentators as public confidence in the country's fourth leader in the last six years erodes.

"The government called a double dissolution election on this issue. To end the year without delivery on its set piece reform would have been disastrous for the government," said Haydon Manning, professor of political science at Flinders University in Adelaide.

Turnbull narrowly secured an election victory in July after he invoked rarely used powers to dissolve both houses of parliament after the upper house Senate repeatedly blocked government legislation on the two bills.

But he has struggled to implement his legislative agenda as his ruling conservative coalition is in the minority in the Senate, requiring Turnbull to win favor with many of the 11 independent senators to pass legislation.

Turnbull led negotiations on the labor bill with independent senators while in Peru this week attending the Asia-Pacific Economic Cooperation meeting, lawmakers told Reuters.

The government continues to trail the opposition Labor Party, a Newspoll on Tuesday showed.

Economic management, a traditional strong point for the conservative government, is now being called into question.

Deloitte Access Economic on Monday forecast Australia's budget deficit to grow by A$24 billion ($17.69 billion) over the next four years - threatening the country's AAA credit rating.

Turnbull now plans to turn his attention towards another cornerstone piece of legislation, which would create a building industry watchdog. The bill was also twice rejected by the Senate in the lead-up to the July 2 election.

The vote for the building regulator in the final two weeks of the 2016 Senate is expected to be tight, one key Senator told Reuters.