The chief of Ontario's Attawapiskat First Nation is nearing the third week of her hunger strike in Ottawa.
The Idle No More movement has been trying to call attention to the federal government's omnibus budget bill over concerns people haven't been properly consulted about First Nations and environmental issues.
Spence wants a meeting with Prime Minister Stephen Harper to discuss the treaty relationship, but so far he hasn't agreed to it.
Aboriginal Affairs Minister John Duncan said he has tried to set up a meeting with Spence, but hasn't received a response.
Shawna Oochoo, who is part of the Regina group, said she's fasting to get an understanding of what Spence is going through.
"This is a huge sacrifice on her part," Oochoo said.
Similar fasts could be held throughout Canada, she said.
The fast in Regina will end with a prayer for Spence and a feast at noon on Dec. 31, Oochoo said.
All month long, there have been Idle No More protests around Canada.
In Saskatchewan on Wednesday, the demonstrations took the form of flash mobs appearing at shopping malls, singing and dancing.