The Collective of National Organisations, made up of nationalistic groups, staged a sit-in for about 45 minutes in front of the Indian High Commission premises here and urged India not to interfere in Lanka's internal affairs.
Several hundreds of them carrying the national flag and staged a prayer before dispersing.
"We pray that India stop pressurising Sri Lanka through the 13th amendment in the same way they put pressure on Sri Lanka 26 years ago", Bengamuve Nalaka, a leading figure in the sit-in, said.
Nationalists now protest Indian opposition to President Mahinda Rajapaksa's move to dilute the 13A by stripping provincial councils of land and police control powers.
Elsewhere, in the central provincial town of Kandy, the All Ceylon Buddhist Congress (ACBC), the prime Buddhist body staged another sit in prayer.
"We pray that India will change its stance as regards 13A so that Sri Lanka can preserve its unity", Prashantha Lal de Alwis, a leading lawyer and a senior ACBC figure, said.
India has repeatedly emphasised to Sri Lanka on the need to fully implement the constitutional provision dealing with devolution of powers to provinces without dilution and to go beyond it to ensure meaningful development there.
Indian leadership expressed "dismay" at Sri Lanka's plan when a group of opposition Tamil lawmakers from Sri Lanka visited the country last month.
