The protest was led by party president Ignazio La Russa and Rome's former mayor Gianni Alemanno, and attended by Italy's former foreign minister Giulio Terzi who resigned in March last year after the marines were returned to India.
Alemanno said Italy's foreign minister Emma Bonino should resign if she failed to bring the marines home and said Rome sever diplomatic and trade ties with India.
"This blow to Italy is truly unacceptable...Italy must break off diplomatic and commercial relations, " he stated.
Salvatore Girone and Massimiliano Latorre were detained in India after allegedly shooting the two fishermen while guarding an Italian oil tanker off the southern state of Kerala in February 2012.
The two marines claim they thought the two unarmed fishermen were pirates and only fired warning shots in the air.
Italy says the incident happened in international waters and the marines should be tried at home while India claims jurisdiction, saying the killings occurred in its own territorial waters.
In a statement last Friday, Italy's prime minister Enrico Letta warned the government would "take all necessary action" to ensure the marines were spared trial under anti-piracy legislation that carried the death penalty.
Letta earlier on Friday held a summit with Bonino after Indian press reports that the marines could be sentenced to death if found guilty under India's SUA Act.
The case sparked a major diplomatic row last year when Italy refused to return Girone and Latorre to India to face trial after New Delhi allowed them home to vote in national elections.
Rome only relented and sent the pair back to India after receiving assurances they would not face the death penalty.
India's interior minister Sushil Kumar Shinde, said on Friday the government would decide in the next few days whether to allow India's National Investigation Agency to filed charges against Girone and Latorre.
The NIA wants to charge the pair under Section 3 of India's SUA Act.