MPs have warned new workplace laws could greatly affect small businesses, as debate continues on the contentious reforms.
The government is attempting to pass its workplace bill, which would allow for multi-employer bargaining, by the end of the year.
But opposition and crossbench MPs have accused Labor of trying to shut down debate.
Debate is expected to run well into the night on Wednesday before a vote in the lower house on Thursday.
The Senate will then have just two sitting weeks to consider the bill before parliament rises for the year.
Independent MP Dai Le said the proposed changes would be a burden for small businesses.
"The bill itself has more layers than an onion, and as you try to peel back you can't help but cry at the layers on top of more regulatory requirement for employers, especially those smaller businesses who can't afford lawyers," she told parliament on Wednesday.
"Why is the government rushing into this with Christmas around the corner, on such important legislation that will have unintended consequences."
Several MPs have backed calls for the bill to split, to ensure that non-contentious elements of the legislation like pay increases for workers could be passed quickly.
Negotiations are still ongoing with crossbench members of the upper house, with independent David Pocock saying he has yet to make up his mind on supporting the bill.
Greens leader Adam Bandt said the minor party would support the bill in the lower house, before considering if further changes needed to be made once debate reaches the Senate.
Labor will need the Greens plus one crossbench senator to pass the bill.
Mr Bandt said he was supportive of many elements of the bill, but wanted to ensure employees would not be left worse off.
"We don't want loopholes in this bill that might allow people to go backwards, and I think that's the government's intention as well," Mr Bandt told reporters in Canberra on Wednesday
"We want to make sure that this bill has a good floor."
The Greens leader said negotiations were continuing with the government.
He said he was happy with the bill's position on multi-employer bargaining with amendments that have been proposed.
Opposition Leader Peter Dutton has called a three-month review of the legislation, rather than it be raced through parliament by the end of the year, along with scrapping changes to multi-employer bargaining.
He warned the bargaining changes would lead to more strike action across the country.
Crossbench MP Rebekha Sharkie has called on the government to expand the definition of small businesses in the bill from 15 to up 100 employees, to ensure that smaller businesses would not be impacted by bargaining changes.
Ms Sharkie also wants an inquiry into the bill's proposal to scrap the Australian Building and Construction Commission
Workplace Relations Minister Tony Burke has insisted the legislation is urgent in order to get stagnant wages moving as soon as possible.
Further amendments to the bill are expected to be debated, with more likely to be considered once a Senate report into the proposed laws is handed down later this month.
"The current bargaining system will not deliver pay equity and the rules they need to be changed," he said.
