President Rudolf Schuster warned the Wednesday demonstrations could lead to a wider social uprising.
Ladislav Fizik, head of a non-governmental group called the Slovak Roma Parliament, said the gypsies' anger at the social welfare cuts made sense in light of their misery.
"The situation in gypsy villages in the east of Slovakia is uncontrollable. They are hungry; they have nothing to eat and that's the whole problem."
But a leader of the gypsy community, also called Roma, said the planned protests over reduced welfare benefits had been cancelled out of fear of violence.
The decision follows another previous protest cancellation on Monday when looting led to 300 or 400 gypsies clashing with police and pillaging of stores in Trebisov in the east of the country.
"Some militants mobilised Roma to loot shops. It was a delinquence which we could not accept," Fizik said.
No one was seriously injured but protesters damaged several police cars by pelting them with stones and bottles.
Police said on Tuesday they had detained 24 people charged with looting a shop in the eastern town of Trhoviste and arrested another 15 in Trebisov.
President Schuster said the reforms had hit hard Slovakia's sizeable gypsy community - estimated at around a half a million people, or a tenth of the population.
Policemen arrest a gypsy protestor
"The harsh cost of social reforms has highlighted the problem of the Roma. Looting shops and other protests of discontent could evolve into a large wave of social agitation."
"I urge the government not to underestimate this social situation and the risks that could threaten reforms and internal political stability."
The benefit cuts in Slovakia, which will join the European Union on 1 May along with nine other mostly former communist states, were introduced this year along with other reforms designed to strengthen the economy ahead of entry.
Under the new system, benefit recipients are obliged to perform 10 hours of community service work per week, or risk a sharp decrease in payments, which have been reduced anyway.
The changes have spurred resentment among Slovak Roma, who since the fall of communism have suffered treacherously high unemployment rates - up to 100% in some villages - and face widespread discrimination.
Under the previous system, a gypsy family with five children could receive monthly benefits totalling €273.
Now it will receive only €260 on condition that both parents do at least 10 hours of community work per week. If they refuse, the family receives €210.
The average monthly salary in Slovakia is around €340.