Read MorePaul Singer: US stocks 'frothy' by 'all measures'
"(A natural EMP event) today would cause a massive disruption to the electric grid, possibly shutting it down entirely for months or longer, with unimaginable consequences," Singer wrote. "Only two years ago, the sun let loose with a Carrington-magnitude burst, but the position of the earth at the time prevented the burst from hitting it. The chances of additional events of such magnitude may be far greater than most people think."
Carrington refers to a solar storm in 1859 that caused telegraph systems to fail around the world.
Singer warned that a man-made EMP attack would be even worse.
"It would not cause any blast or radiation damage, but such an attack would have consequences even more catastrophic than a severe solar storm. It could not only bring down the grid, but also lay down a very intense, very fast pulse across the continent, damaging or destroying electronic switches, devices, computers and transformers across America," the letter said.
A spokesman for Elliott declined further comment.
The letter called on leaders to protect the power grid and essential electronic devices. He also said that spare parts should be stockpiled and that government and other groups should prepare an emergency response plan.
"Why are we writing about this topic? Because in any analysis of societal risk, EMP stands all by itself. Congressional committees are studying this problem, and federal legislation is laboriously working its way through the process," the letter said. "We think that raising people's consciousness about what should be a bipartisan push to make the country (and the world) safer from this kind of event is a good thing to do."
Read MoreNotorious Doomsday Prophets