Small businesses would have no choice but to pay around $15,000 to take part in multi-employer bargaining under the federal government's new workplace relation laws, the coalition says.
They've labelled that cost a "small business bargaining tax" as they ramp up their opposition to Labor's bill.
The bill's regulatory impact statement says multi-employer bargaining will cost small businesses around $15,000, while it would cost medium-sized businesses around $70,000.
But Small Business Minister Julie Collins said around 90 per cent of all Australian businesses are exempt from the single-interest stream bargaining system.
"Many businesses already incur costs and many businesses are already covered by their employer peak organisation," she told parliament.
"Our expectation is most small businesses would be in the co-operative stream where they can use off-the-shelf agreements."
Ms Collins added small businesses would be supported through the bargaining process by the Fair Work Commission.
The government has put aside about $8 million across four years to help small businesses transition to their new systems.
Business Council chief executive Jennifer Westacott said compliance costs for small and medium businesses were set to "explode".
"Make no mistake, the expansion of multi-employer bargaining will not increase wages but it does open the door to more strikes and more disruption," she said.
"At a time of global economic uncertainty, skyrocketing inflation and a global cost of living crisis, Australia has almost full employment and wages are beginning to strengthen,why would we take this risk?"
Independent MP Zoe Daniel used parliament to ask Workplace Relations Minister Tony Burke if the 15-person headcount for a small business needed to be lifted.
"There would be thousands of small businesses across the country potentially drawn into multi-employer bargaining," she said.
"Overall, I supported the bill, however, does the government accept the numbers should be raised to a higher number of full-time equivalent staff?"
Mr Burke said it was an element of the act that remained in negotiation with the Senate crossbench.