The Morrison government's $4 billion hiring credit for young workers is expected to pass parliament this week.
However, Labor and cross benchers remain concerned it is not ambitious enough to deal with the jobs impact of the coronavirus pandemic.
The JobMaker hiring credit will provide $200 for organisations to take on a 16 to 29 year old employee and $100 for 30 to 35 year olds.
Given the higher rate of joblessness for young people and the potential for them to be trapped in welfare for long periods, business groups and economists have backed the plan.
Unions say there is no strong policy basis for putting an age limit on the plan, with many over-35s expected to face a tough 2021 in terms of finding work.
There are also concerns about insufficient safeguards against unscrupulous employers replacing secure, full-time workers with insecure part-time and casual workers.
A bipartisan report into the laws recommended they pass parliament.
But Labor senators noted the hiring credit lacked ambition in driving down unemployment quickly.
Labor frontbencher Brendan O'Connor said the party supported wage subsidies but would work through the detail of the laws.
"We're concerned that this government inflates its announcements, but fails to follow up, just like it inflated the number of jobs the hiring credit will create, which turns out to be just 10 per cent of their promised 450,000."
Labor wants to see an evaluation of the scheme early in its operation and the release of comprehensive data showing its impact.
Independent senator Rex Patrick said the bill should not be passed in its current form as it would be "in breach of constitutional conferral of legislative power on the parliament".
The Greens also object to the bill as it stands.
They are planning amendments to ensure businesses can't get the credit if they are found to be underpaying their workers, and to put in place a process to allow workers who are fired or have their hours reduced to dispute the decision.
With both houses of parliament sitting from Monday to Thursday, the lower house will deal with welfare measures, native title changes and a new scheme to boost checks on foreign investment.
On Monday, a Senate estimates committee will hear further evidence from Australia Post following the resignation of CEO Christine Holgate over the Cartier watches scandal.
And on Wednesday, the chambers will briefly suspend to mark Remembrance Day.
NAIDOC Week will also be marked.