Several senior officials in the largest state-run tourism organisation in Cuba Cubanacan have been placed under house arrest on suspicion of corruption.
Cuba is keen to attract American tourists
Among those detained is the president of Cubanacan, Juan Jose Vega.
Millions of dollars are said to be missing from the hotel, restaurant and travel agency business.
The irregularities came to light when the company complied with a government order to all firms holding US dollars to convert them into Cuban pesos.
For weeks Havana has been awash with rumours of a major corruption scandal unfolding, the BBC's correspondent in Havana, Stephen Gibbs, says.
Castro hopes tourism will help prop up Cuba's troubled economy
He says that government sources have now confirmed to the BBC that the investigations centre on Cubanacan.
With its president under house arrest, the group is now being directly managed by Cuba's minister of tourism.
Cuban Minister of Defence Raul Castro is reportedly taking an active involvement in this inquiry - this points to the seriousness of the allegations, our correspondent says.
Temptation of corruption
The scandal apparently came to light after a recent change in the rules in Cuba, whereby local firms had been told that they could not hold US dollars.
In the process of exchanging their holdings into Cuban pesos, shortfalls were apparently uncovered.
Since the demise of its Soviet backer in the early 1990s, Cuba has legalised the dollar and turned to tourism to save its economy.
In the process, the flow of hard currency into this communist-led island has increased - and so has the temptation of corruption, our correspondent says.