Representatives of both companies have been tight-lipped so far on the proposed dam’s construction.
In their letter, SRP lawmakers said more than 29,000 people from four different provinces had signed a petition.
She’s been featured in a documentary of inspiring girls around the world and has even met with US First Lady Michelle Obama.
The market was opened in 1937, it has 3,000 shops, ranging from stationary and electronics, to rice, meat and trinkets for tourists.
Moeung Sonn, who has fled the country, is facing a two-year prison sentence following a suit brought by the government in 2009.
The BBC World Service Trust surveys 2,401 Cambodians from all walks of life.
About 60 million people depend on the Mekong directly or indirectly for their livelihoods.
At least eight hydroelectric dams have been proposed on the upper Mekong River.
Critics of the dam say it will hurt ecosystems in the river that provide a major source of fish for Cambodians.
Some say the connection between rural and urban areas across borders in the Mekong countries can help boost economies across the region.
Opponents say the dam could be damaging to the ecology of the river and the livelihoods of the people who rely on it.
Phnom Penh has around 5,000 families in slum areas with free access to safe water.