An outsource call centre operator for Centrelink paid no corporate tax for several years even after winning a major government agency contract worth tens of millions of dollars, Guardian Australia can reveal.

The Perth-headquartered company, Telco Services Australia, generated more than $185m in revenue in 2024-25 but reported no taxable income, new financial documents show.

The year before, it reported $130m in income and also paid zero tax.

The two-year reporting period coincides with the company’s multi-year $90m-plus contract to run call centre operations for Services Australia, the agency responsible for social security.

Jason Ward, the principal analyst at the Centre for International Corporate Tax Accountability and Research, said the business appeared to be structured in ways “to have avoided reporting and tax obligations in Australia”.

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He said the federal government should subject those bidding for public contracts to higher levels of transparency.

The financial documents, lodged on Christmas Eve, show that there were $166.5m in related party transactions last financial year at Telco Services. There is no detail about the identity of the related parties.

These payments “virtually eliminate profits” for the company, according to Ward, resulting in no tax payable.

At the same time, payments for directors and key management personnel increased during the 12-month period, the documents show, even after it reported a financial loss.

There is no suggestion the company or its directors have acted illegally.

Telco Services is one of the operational arms of a Perth-based entity known as TSA Group, run out of Perth. The group says it has a team of more than 4,300 workers operating in five contact centres across Australia and the Philippines.

Along with its government agency contract, the group runs outsource operations for major corporations and brands, including Telstra and NRMA insurance.

A TSA group spokesperson said while the Telco Services company did not record taxable income, “other associated entities did and the appropriate amount of tax has been paid by them”.

“The taxation arrangements and payments have been assessed by a large, independent auditor,” the spokesperson said.

The spokesperson said the entities which paid the tax were not required to meet public reporting requirements and that Telco Services had paid tax in prior years.

TSA described the related party transactions as costs incurred for services provided by associated companies, which are “simultaneously booked as revenue by the associated companies”.

An analysis of the TSA group’s structure by Guardian Australia found that its various businesses rarely lodge public financial accounts, which is unusual for such a large operator with thousands of employees and large revenue streams.

The complex structure made it impossible to publicly verify how much overall tax it has paid, or how related party transactions flowed between different entities.

Another of its operational arms, called Telco Sales, holds a flagship contract with Telstra. This company paid just over $700,000 in corporate tax in 2022-23 but received a partial refund the following year. It generated more than $120m in revenue over the two tax years.

While the Telco Services arm of the TSA group holds the Services Australia outsource contract, the staff are employed by a different entity called Trimatic Management Services.

Trimatic received $5m in grant funding from the Western Australian government in 2024 to expand call centre jobs in the state.

A spokesperson for Services Australia said the agency hosts one of the largest contact centre networks in the country and that its workforce is “built on a base of mostly permanent Australian public service staff” supplemented by contractors.

Centrelink also uses a separate outsource operator, Concentrix, to run some of its call centre operations.

Guardian Australia has detailed over recent months how heavily government agencies now rely on outsource call centres and how attempts to curb reliance on external consultants and contract workers have stalled.

The majority of calls to the Australian Taxation Office’s phone line are answered by workers at three private operators, the US private equity-owned Probe Operations, British multinational Serco and Concentrix.

Tax agents have complained to the ombudsman of a deteriorating service on the ATO phone lines, saying they often speak to inexperienced call staff who cannot provide informed responses.

Do you know more? Email jonathan.barrett@theguardian.com