"Nitish Kumar first got permission from the government but was stopped and asked to defer his visit. Why was Nitish stopped from going to Nepal? We are not pressing for a notice but want the government to clarify," Janata Dal United MP Sharad Yadav said in the Lok Sabha.
Sources say Mr Kumar's visit this week was stalled at the last minute. The Bihar government was reportedly informed about the change of plans by Foreign Secretary S Jaishankar on Sunday.
Mr Kumar wanted to visit Janakpur near Bihar's border with Nepal, which is around a half-an-hour chopper ride from Patna.
"This smacks of politics by the BJP even in relief work out for earthquake victims," said the party's KC Tyagi, claiming that details of Mr Kumar's visit had been given to Nepal as well as the Centre well in advance.
Nitish Kumar has not reacted officially, but sources say he had commented to his party colleagues that he would have been more surprised, had he been allowed to make the trip.
Bihar has been at the centre of Indian relief and evacuation efforts after the April 25 earthquake that killed over 7,300 in Nepal and at least 60 in Bihar.
Nitish Kumar had appreciated the Centre's relief operations, a move that was noticed as he has long been a critic of Prime Minister Narendra Modi.
"He wanted to go to Janakpur to express solidarity with people there, most of them are from Bihar. But there seems to be politics in asking Nitish Kumar not to go to Nepal," Mr Tyagi said amid speculation that the PM Modi-Nitish Kumar rivalry had played a role.