In an opinion piece in Saturday's The Canberra Times, the senator says she had to make a deal to help the government repeal a law that allowed doctors to authorise medical evacuations from offshore detention centres.

That deal was helping "make a huge difference" to the lives of asylum seekers in offshore detention, she said.

"The problem I'm facing is that the agreement I made gets torn up if I reveal it," Senator Lambie writes.

"To work, the people affected can't know."

The repealed law allowed two treating doctors, rather than the government, to decide if a detainee should be evacuated to Australia.

Prime Minister Scott Morrison has consistently denied a deal was made to give back control over the evacuations.

As recently as last month, Senator Lambie was also denying there was a secret deal, and earlier cited "national security".

"Every day I'm forced to keep this secret, I'm struggling," Senator Lambie now says.

"I've lost fans and friends over this, some of which I'll never get back."

The senator said the people most offended by her secrecy were those who cared the most about the wellbeing of asylum seekers.

"If you care about what's good for the country, you don't want me to reveal the deal," she writes.

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