They are among 13 women sentenced last month by a Phnom Penh court to two and half years in prison for aggravated rebellion and illegal occupation of land. They claimed the government broke promises to give them new land.
The women were arrested when they tried to rebuild their homes on the land where their houses were demolished by developers in 2010. They lived in Phnom Penh's Boueng Kak lake area, which the government awarded to a Chinese company to develop a hotel, office buildings and luxury houses.
The Housing Rights Task Force said the four women began a hunger strike on Sunday to demand their immediate release.
In Cambodia, land grabbing is sometimes linked to corruption and the use of deadly force.
Long Kim Heang, a communications officer for the Housing Rights Task Force, said the group learned of the hunger strike from relatives of the strikers who visit them almost every day.
However, an officer at Prey Sar prison where the women are being held, said the woman are eating normally and not on a hunger strike. The prison officer spokes anonymously because he is not authorized to speak to the media.
Since their eviction, the women had protested persistently, though public dissent is discouraged under the government of Prime Minister Hun Sen. Their families and neighbors have held several demonstrations of support for them.
On Monday, about 100 of them demonstrated in front of the Royal Palace to urge King Norodom Sihamoni to help obtain the release of the women. Their petition was accepted by a palace official, but any subsequent action was unknown.