Wiper Leader Kalonzo Musyoka has called on President William Ruto to disclose the details of his recent trip to the United States.
Kalonzo questioned the President's decision to use a private jet instead of the national carrier and said that this move should be closely scrutinized.
In a statement on X, Kalonzo said that the opposition must raise such concerns.
"I challenge President William Ruto to lay bare all the facts regarding his recent overseas trip to the US. The money used to hire the Dubai private jet vis-à-vis using our National Carrier Kenya Airways needs further examination," Kalonzo said.
The President travelled to the US aboard an A6-RJU royal jet for a three-day state visit.
On Sunday, Ruto defended his move saying that the cost incurred for his travel to the US was way less than what would have been spent if he had used a Kenya Airways plane.
Ruto said the choice of his plane to the US was influenced by his decision to ensure the prudent use of State resources.
"Fellow Kenyans, I have noted concerns about my mode of transport to the USA. As a responsible steward of public resources and in keeping with my determination for us to live within our means and that I should lead from the front in so doing, the cost was less than travelling on KQ," Ruto said.
Ruto, however, did not state the amount he used for the hired jet and the amount he would have spent if he had to use a Kenya Airways plane.
A State House official had earlier told the Star the President could not use his presidential jet as it has never been to the US since it was bought in the 90s.
The official said the design of the jet makes it effective to operate in Europe, Africa and the Middle East.
State House Press Secretary Emmanuel Talam was quoted by local media saying the plane could not be used as "it will have to stop five times to refuel".
Kalonzo further raised concerns with Ruto's stance on sending police to Haiti.
According to the Wiper leader, the move defies the high court orders.
"The deployment of 1,000 police officers to Haiti despite a Justice Chacha Mwita judgement that deemed such actions as illegal and unconstitutional, is in contempt of the High Court," Kalonzo added.
"As the government-in-waiting, we will be failing Kenyans if we do not raise these fundamental concerns. We must as a Nation advocate for the truth."