Australia's competition watchdog will be given far stronger powers to prevent companies from making repeated under-the-radar acquisitions that could harm competition and consumers.

The changes, being announced by Treasurer Jim Chalmers on Wednesday, are the biggest reforms to merger settings in almost 50 years and were one of several options flagged in a Treasury consultation paper late last year.

From January 2026, the onus will be on companies to notify and then convince the Australian Competition and Consumer Commission (ACCC) that proposed mergers and acquisitions above a certain threshold would not substantially lessen competition before they could progress with deals.

Decisions would also be subject to review by the Competition Tribunal.

"These changes mean the ACCC will more efficiently and effectively target mergers that are anti-competitive, while allowing mergers that are pro-competitive to proceed faster," Mr Chalmers will say in a speech in Sydney on Wednesday.  

"This will bring our merger settings into the 21st century."

Jim Chalmers says the merger regime will be more efficient. 

To allow the regulator to review more mergers and acquisitions before they happen, "cost recovery fees" will be introduced, whereby higher-risk mergers face higher fees.

Treasury expects fees to be between $50,000 to $100,000 for most mergers, but small businesses will be exempt.

Last year, over 1,400 mergers were recorded, at a value of about $300 billion, but only about 330 were notified to the ACCC under the existing voluntary merger regime.

About half of the mergers are made by the largest 1 per cent of businesses.

"Some mergers can cause serious economic harm," Mr Chalmers will say during the Bannerman Competition Lecture, hosted by the ACCC and the Law Council of Australia.

"This happens when players are not interested in improving profitability by lifting productivity.

"When they're solely focused on squeezing out competitors to capture a larger percentage of the market."

Mergers to be 'fast-tracked' and there will be a public register

The move follows years of claims by former ACCC chair Rod Sims and his successor, Gina Cass-Gottlieb, that Australia's merger regime is not fit for purpose and lags those of other developed economies.

Australia is one of only three OECD countries with a voluntary regime, along with the United Kingdom and New Zealand.

The ACCC's calls for merger reform have been met with resistance from some business groups and their lawyers who argue the changes to make ACCC approval mandatory would stop mergers going ahead.

But the ACCC has argued that most mergers don't have an impact on competition as the regulator waves through more than 90 per cent of proposals.

Ms Cass-Gottlieb says stronger merger laws are critical to ensure anti-competitive mergers do not proceed and the changes will benefit Australian consumers and businesses.

"These proposed changes are significant and will reinforce public confidence in Australia's competition laws," Ms Cass-Gottlieb said.

She said currently Australia's merger regime does not require merger parties to notify the ACCC of proposed acquisitions or to wait for ACCC clearance before proceeding.

The competition regulator is currently reviewing Sigma's proposed $8.8 billion merger deal with pharmacy retailer Chemist Warehouse.

The ACCC also welcomed changes to better deal with serial acquisitions, where several smaller transactions occur over time that can result in serious harm to competition.

Mr Chalmers will argue the new reforms will make Australia's merger approval regime "faster, stronger, simpler, more targeted and more transparent".

"It will be faster because most will now be approved within 30 working days, where the ACCC is satisfied a merger poses no threat to competition," Mr Chalmers will say.

"It will be stronger because we are legislating a mandatory notification system and empowering the ACCC as the single decision maker on all mergers."

Mergers above monetary thresholds and which would significantly change market concentration would need to be notified to the ACCC and be approved before proceeding. These thresholds will be based "on international practice and set through consultation".

"It will be simpler because we are reducing three streams to a single, streamlined path to approval that removes duplication and standardises notification requirements for all mergers," Mr Chalmers will say.

"It will be more targeted because mergers that create, strengthen or entrench substantial market power will be identified and stopped while those consistent with our national economic interest will be fast-tracked.

"Finally, the merger regime will be more transparent, by ensuring the ACCC has better visibility of merger activity."

The federal government would also create a public register of all mergers and acquisitions, and these would be notified to the ACCC to promote transparency and accountability.

Some companies have been flying under the ACCC's radar

The ACCC has argued that under existing laws, even if it believes a proposed merger or acquisition will harm consumers, there is little it can do to stop it from going ahead. It can challenge mergers in court, but only after they happen. 

This has allowed some companies to fly under the radar, and to not notify the ACCC of deals.

The consumer watchdog has previously singled out retail giant PETstock completing a spate of pet shop and vet clinic acquisitions that it did not notify the regulator of. The ACCC did not even become aware of this until much later when Woolworths sought approval to acquire PETstock.

Aviation giant Qantas has also previously bought a stake in several small airlines without giving the ACCC notification.

Reviews of ACCC decisions will be the responsibility of the Competition Tribunal, made up of a Federal Court judge, an economist and a business leader.

The government will consult with stakeholders to finalise the details in advance of the new system beginning in January 2026.

"Right now, merging businesses do not have to notify the ACCC or wait for the ACCC's view before completing a merger," Mr Chalmers will say.

"Our voluntary system means the ACCC isn't properly equipped to detect and act against anti-competitive mergers."

"It has limited visibility of merger activity and doesn't always see the ones that present the greatest risks to competition."

Mr Chalmers says the changes are the product of detailed discussions, led by the Competition Taskforce, and overseen by an expert advisory panel comprising business and regulation experts including Kerry Schott, David Gonski, John Asker, Sharon Henrick, John Fingleton, Danielle Wood and Mr Sims.

Mr Chalmers says while companies would be required to notify the ACCC about mergers and acquisitions there wouldn't be a higher hurdle for them to get approval. 

"We won't be changing the ACCC's test to 'reverse the onus of proof', a change some in the business community opposed," he will say. 

Another issue that has had business groups concerned is that the ACCC has relied on the fact it can block deals based on hypothetical future outcomes.

Recent decisions such as Transurban's failed bid to acquire Melbourne's EastLink motorway were opposed by the ACCC.

And while ANZ has won its fight to overturn the competition watchdog's decision to block its $4.9 billion acquisition of Suncorp Bank, the sale is not a done deal.

Some in business had wanted the government to go with the Treasury consultation paper's other option to overhaul merger laws, including a US-style proposal that would greatly curb the regulator's powers. Under that option, the Federal Court would have become the default decision maker for deals questioned by the ACCC.

But now that the government has decided the ACCC will be the ultimate decision maker, and Mr Chalmers says they want to see more economic experts brought in.

To that end, the government will be appointing Philip Williams AM, a former professor of law and economics at the University of Melbourne, as a commissioner from June 27.

The federal government will also release an updated ACCC Statement of Expectations, setting out what it expects of the regulator in relation to consumer matters, competition enforcement, and telecommunications sector oversight.