The network called for a day of action against those investments, scheduled to take place in November, as part of a new campaign to shift financial investments from fossil fuels to clean energy.
While he admits nearly every major investment bank has investments in coal, Matt Leonard, a global finance campaigner for the network and the study's lead researcher, said Citi and Bank of America are above average in coal investments.
As he looked through the 150 proposed coal-fired plants on the table in the United States, the names of Citi and Bank of America kept coming up as underwriters, he said.
"They are the largest banks investing in coal and they are two banks that have been vying for the consumer recognition of being 'the green bank,'" he said. "We applaud that they are trying to be 'the green bank,' but we want it to be meaningful and not just a thin veil of tokenism."
In a statement, Citi did not address its coal investments, but said it is taking "a responsible and strong leadership position on climate change."
Aside from committing $50 billion to combat climate change over the next 10 years, Citi said it has committed to reducing its own carbon emissions by 10 percent and is investing in climate-friendly enterprises, among other things.
Bank of America pointed to the $20-billion environmental initiative it introduced in March.
"The reality is as a country over 50 percent of the electricity we all consume comes from coal," said Ernesto Anguilla, spokesperson for Bank of America. "Bank of America is aggressively investing in financing the development and use of cleaner, renewable energies."
Coal has come under fire in the last few weeks, as the U.S. Environmental Protection Agency fined a utility for its coal-based emissions and the New York attorney general began investigating whether five energy companies disclosed all the climate-change-based financial risks of their coal-fired plants (see Coal Under Fire).
But the network said the United States is in the middle of a "coal rush."
"There had been a bit of a lull in new coal-plant development, but that has changed," Leonard said. "Right now, there are about 150 proposed plants on the drawing board, and that's a huge explosion from the last five to 10 years. At precisely the time scientists are saying we have to reduce emissions, the U.S. is poised to increase emissions."
The network wants the nation's banks to spend the roughly $140 billion potentially headed to coal plants on renewable energy and energy efficiency, he said.
While other fossil fuels also are part of the problem, Leonard said coal is the network's "overarching concern."
"Coal is overwhelmingly the No. 1 cause of climate change and coal reserves in the ground are enough to put the world well beyond any tipping point," he said.
Aside from solar and wind, some entrepreneurs think so-called "clean coal" technologies could play a role in bringing the United States energy independence while reducing emissions.
One such company, GreatPoint Energy, closed a $100-million round last month.
But the concept is controversial and Rainforest Action Network doesn't think that so-called "clean coal" technologies will make a difference.
"Any fossil fuel is an unsustainable source that's inherently dirty," Leonard said. "We really need to be refocusing that effort and capital into renewable energy."