A landmark deal allowing South Australian employers to cut weekend penalty rates has lost traction only months after it was brokered, with no businesses adopting the voluntary change.

The Shop Distributive and Allied Employees' Association (SDA) struck the template enterprise agreement with Business SA in March after nine months of negotiation.

Under the deal, which was to be voluntary for both the employer and the employee, Saturday penalty rates were to be abolished and Sunday rates halved.

At the time, the union said employers would be better off under the deal, which offered significantly higher base rates of pay, guaranteed annual pay rises and improved rostering and shift breaks.

But Business SA's Nigel McBride on Tuesday said no businesses had signed up to the agreement so far, despite many exploring it as an option.

"It's disappointing but I can't blame small businesses who feel like the marginal gains aren't worth the costs and the risks," Mr McBride said.

He said the result probably showed some businesses were put off by the complicated process of registering an enterprise agreement and the fear they would be targeted by unions.

Mr McBride said the negotiations had not been a waste of time because businesses could still sign up to the deal.

National penalty rates review needed: Business SA

The group has called for a national review of penalty rates.

"We believe penalty rates need a full overhaul," Mr McBride said.

"This was an interim step to try and get some marginal relief for some small retailers, who particularly needed to open on Sundays and public holidays.

"We need a national overhaul of penalty rates. We don't want to remove penalty rates, we just want them to be a lot more sensible in an economy which is under a huge amount of pressure."

Union secretary Peter Malinauskas said he was surprised businesses were not interested.

"We're disappointed that there aren't more fair-minded employers who want to take a consensus-driven approach when it comes to restructuring penalty rates," Mr Malinauskas said.

"Many employer associations want their cake and eat it too. They want penalty rates to be reduced but they are not willing to give workers any offsets for it."

He said the union was "fiercely opposed to" employers cutting rates without anything in return.