Supporters of the so-called Medevac legislation will gather on the lawns in front of Parliament House later on Sunday to hold an overnight vigil ahead of senators returning to Canberra.
The Medevac legislation allows the temporary transfer of patients in offshore detention centres for medical treatment or assessment, laws the Morrison government now wants to overturn.
Senators are due to vote on the repeal bill this week.
Former independent MP for the Victorian seat of Indi Cathy McGowan, who was instrumental in getting the laws passed in the last term of parliament, will be in attendance, along with religious leaders.
"This lifesaving law has meant that doctors, not politicians decide the treatment for people detained offshore," National President of Rural Australians for Refugees Louise Redmond said in a statement.
"So as politicians return to Canberra ahead of the crucial vote, we're going to make sure it's the voices of quiet Australians from the bush they remember as they walk through the halls."