Italy warned India this week that a trial could force a reaction from Italy and the European Union if the trial goes ahead.
The marines were part of a security detachment aboard the oil tanker Enrica Lexie protecting the vessel from pirates off the southern Indian state of Kerala in February 2012.
They are accused of shooting two Indian fishermen after mistaking them for pirates.
Italy maintains the Indian fishing boat behaved aggressively toward the Enrica Lexie and ignored warning shots from the guards.
India's Supreme Court said last week it will meet Feb. 18 to decide if the two marines, Massimiliano Latorre and Salvatore Girone, can be tried under maritime security law.
Italy, which has been fighting for the charges to be dropped, reacted angrily Monday to the news that India's Supreme Court will hear the case, the BBC reported.
The office of Italy's Prime Minister Enrico Letta issued a statement saying if the case proceeded, it would have "negative consequences in relations with Italy and the European Union, with equally negative repercussions on the global fight against piracy."
The marines were facing the death penalty if convicted, but India's Home Ministry announced Thursday it had dropped charges that would have meant a mandatory death penalty, the Times of India reported.
Instead, the Home Ministry has ordered the National Investigation Agency, which is investigating the case, to seek conviction on lesser maritime security charges that would carry a maximum prison sentence of 10 years along with a fine.
The Times also reported that Latorre and Girone expressed regret over the deaths, but they continue to proclaim their innocence.
"We regret the loss of two human lives, but we don't feel we are responsible at all, we are innocent," the marines told Italian state broadcaster Rai in New Delhi. "The accusation of terrorism is deeply painful for us, not only as military men, but as parents and human beings."
A civil case over the shooting deaths was settled in late April 2012 when each family of the dead fishermen accepted around $190,000 as compensation and for dropping the charges, Press Trust of India said.
But Indian authorities didn't drop the criminal case, which has dragged on straining diplomatic relations between the countries.
The European Union has been urging India and Italy to reach agreement over the impending trial.
The Indian newspaper Economic Times reported last month the EU issued a statement saying the outcome could affect the fight against piracy on the high seas.
"We, the European Union, encourage India to find as a matter of urgency a mutually satisfactory solution to this long-standing case in accordance with international law and U.N. conventions on the law of the sea," Maja Kocijancic, spokeswoman for EU foreign affairs chief Catherine Ashton, said.
"This issue also has a bearing on the issue of global fight against piracy to which the EU is strongly committed. We will continue to follow the case," she said.
Piracy in the India Ocean has been a major problem for commercial shipping between India and the eastern African coast, particularly in the Arabian Sea, with many hijackings and crews being held for ransom.
Many shipping operators have hired armed guards to sail aboard their ships.
But the policy of using armed guards has been controversial, with fears of crew members being caught in deadly cross fire between hired security staff and pirates attempting to board a vessel.