From Tuesday, construction, security, cleaning and traffic companies who want to vie for ACT government work will have to hold a Secure Local Jobs Code certificate, which requires them to be audited at least every 18 months to ensure they have not underpaid their staff.

The companies also have to comply with the code, which requires them to hand over addresses, working hours and contact details associated with the work to a Secure Local Jobs registrar, so unions can exercise their right of entry. Employers also have to give new employees union membership forms to be code-compliant.

So far, just 37 businesses have obtained a certificate from across the four industries. A total of 55 applications have been filed.

But the tenderers in this small pool will soon be the only ones able to tender for ACT government work in those four industries, and tenders that should have gone out last year were purposefully delayed so only code-certified companies could apply.

An ACT government spokeswoman confirmed that a number of long-term contracts for existing services that were due for renewal in late 2018 were deferred until the code became operational.

"Interim arrangements have been put in place to allow new tenders to be undertaken following the commencement of the Secure Local Jobs Code," she said.

"One tender was recalled in late 2018. The delegate decided to delay the tender until the Secure Local Jobs Code was implemented. This decision was made to ensure a fairer procurement process and better outcomes for Canberra workers.

The government did not respond to questions about how many tenders were delayed, nor the value of those tenders. The spokeswoman also did not state what the value of the recalled tender was.

It is also not clear what the tenders were for, or what industry they related to.

ACT opposition industrial relations spokesman Andrew Wall said he remained concerned about the introduction of the code.

Mr Wall has been contacted by business owners who believe the code is too onerous and takes away the scalability of their operations.

He said one had told him it was "not viable to do business with the ACT government anymore".

"The fact only 37 businesses are compliant across the four sectors is deeply concerning and raises questions about how we will get value for money for taxpayers," Mr Wall said.

"If only 37 are qualified it also indicates delays on the government's part in allowing business to go through certification, but also signals barriers for businesses signing up to the new code and taking on government work."

Eight businesses have also applied for an exemption from the code, although none have been approved so far.

The exemption exists for companies caught between the ACT code and Commonwealth laws like the Federal Building Code.

There was concern parts of the code - like allowing union workplace delegates paid time to attend union training or industrial tribunals - could be seen as giving union members more benefits in the workplace,  thus breaching the freedom of association provisions of the Federal Building Code.

However the Australian Building and Construction Commission said it was possible for businesses to tread a fine line between both codes.

“While there may be some potential for conflict between the ACT code and the Commonwealth code, subject to how contractors implement the ACT code, it is possible to comply with both codes," a spokesman said.

“The [commission] is available to provide advice and assistance to contractors in relation to their particular circumstances.”