Crossbench senator Rex Patrick has launched a push to shut a 25-year-old loophole exempting more than 1100 companies from reporting to the corporate watchdog.
Under the plan, the large proprietary firms would be forced to meet Australian Securities and Investments Commission reporting requirements.
The change has been tacked on to a government bill granting a one-year extension to financial advisers to complete a mandatory exam.
That triggered a parliamentary stalemate for the second time in as many weeks, with the upper house voting to restore Senator Patrick's amendment after it was knocked off in the lower house.
"It's been rejected because the government want to protect their mates," Senator Patrick told parliament on Monday.
"They want to protect their very wealthy mates that provide them with political donations and the time has come for that to stop."
Assistant Financial Services Minister Jane Hume said Senator Patrick's amendment was unrelated to the time-critical bill.
She also defended the government's record on making firms pay tax.
"This government has effectively been tackling multinational tax avoidance, transparency and accountability for companies of all sizes," Senator Hume said.
If the bill passes, financial advisers will have until the start of 2022 to pass the exam and until January 2026 to get an approved tertiary degree.
Debate was adjourned until Tuesday.