Unions at the French department store Printemps have asked authorities to open a probe into what they call opaque finances in the sale of the luxury shop chain to investors from the gas-rich Gulf state of Qatar.

"We have turned to the prosecutor because we have discovered multiple financial arrangements in the sale specifying exorbitant commissions and intermediaries which also get exorbitant sums," said Bernard Demarcq, the spokesman for the unions at the store chain.

"All this seems very opaque to us. This should be probed for possible corruption, breach of trust, money laundering and tax fraud," he added of the request submitted Tuesday.

According to documents seen by AFP, a group of Qatari investors will via a Luxembourg firm called Disa buy out the 70 percent shareholding of Deutsche Bank and the 30 percent owned by the Italian Borletti Group.

The value of the transaction, which should be finalised by the summer, was not detailed in the document. But one media report said the deal could be worth around €1.6 billion. The transaction is expected to be completed within months.

There are 16 Printemps stores in France, including the flagship Printemps-Haussmann shop in central Paris, with employ some 3,400 people.

France has proved attractive to Qatari investors who have bought Paris Saint-Germain football club and acquired three percent of energy giant Total as well as stakes in building firm Vinci and in media group Lagardere, although the investments have provoked some criticism among the French public.

Around 10 percent of Qatari foreign investments are in France.