ADP said Royal Schiphol had sold off the shares at a price of 133 euros per share - a sharp discount to ADP's closing share price of 147.65 euros on December 5.

ADP added that the proceeds from this transaction to Groupe ADP amounted to around 420 million euros ($440.2 million).

ADP shares were down 13.68% at 127.05 euros in early session trading - the worst performer on France's SBF-120 index. The French state owns just over 50% of ADP's share capital.

"The sale of multiple smaller stakes and a block trade implies in our view there were no strong candidates for the whole stake," RBC said in a note.

It "is therefore more negative in terms of sentiment and catalyst for ADP stock price than could have been," the brokerage added.

Royal Schiphol had already sold in November a 2.5% stake in ADP to Credit Agricole and a 1.6% stake to Canada Pension Plan Investment Board.

($1 = 0.9542 euros)

(Reporting by Clement Martinot and Dominique Vidalon; Editing by Jacqueline Wong/Sudip Kar-Gupta)