It says both the BNP and the Awami League have always opposed them while in power and supported them when in the opposition.
Bangladesh has signed a deal with India to set up the 1,300-megawatt thermal power plant at Bagerhat's Rampal, near the Sundarbans.
The two countries will have equal partnership in the venture styled Bangladesh-India Friendship Power Company Ltd.
Leftist parties, under the banner of Oil Gas Committee, have been opposing it, saying that the coal-fired power plant will threaten the ecological balance of the largest mangrove forest in the world.
The government, however, insists that proper measures will be taken to protect the environment from pollution.
"We will press ahead with our movement to save the Sundarbans with the people and will not stop until the government calls off the project," Oil Gas Committee Convener Sheikh Shahidullah told a media briefing on Monday.
Last week, the BNP came out with support for the movement. At a press conference, Chairperson Khaleda Zia slated the project and demanded the power plant be relocated.
On Saturday, Prime Minister Sheikh Hasina appeared before the media and claimed that the demonstrations against the project were patronised by the BNP. The Awami League president said it was for this reason that Khaleda was supporting the protests.
"(Because) the party had inked deals against national interest when they were in power," said the platform's Member Secretary Anu Muhammad. "We have been protesting against this for quite some time now. It's good that she (Khaleda) realised it. But a joint movement is out of the question."
Referring to Hasina's remarks, he said they had enjoyed support of both the BNP and the Awami League in their movements over the last 10 years.
"The prime minister is trying to take advantage of Khaleda's support to smear our movement. We want to say it clearly that not only the BNP, but we also have had the privilege of being supported by the Awami League during the last ten years."
Recalling the 2006 movement opposing open-pit mining at Dinajpur's Phulbarhi coal mine, Anu said, "The Awami League had backed our movement, when the then BNP-Jamaat alliance government ordered police to open fire on protestors."
He said the government of the day had also claimed the protestors were patronised by the opposition.
"When these parties are in power, their role is simply the opposite, which's clear from how the government is responding now."