Fiat said it intends to raise its stake in Chrysler by 3.3 percent, taking its holding to 68.49 percent once the operation is completed.
It estimated the price of the most recent stake at €198 million but said it was awaiting a US court decision on the price.
This is the third purchase operation by Fiat of its kind over the past year. The Italian company currently holds a 58.5 percent stake in Chrysler.
The purchase is from the Veba pension fund of the US auto union UAW, which holds 41.5 percent of Chrysler.
Fiat wants to merge with Chrysler as soon as possible.
Fiat last week went to court in the US state of Delaware over a dispute on the price of another 3.3 percent stake it wants to buy.
The ruling could be key to future operations.
Fiat and Chrysler chief executive Sergio Marchionne was quoted by Italian media as saying: "If they accept our payment, we can conclude in a week".
Fiat took operational control of Chrysler in 2009 and took a majority stake in June 2011 but the two groups still operate independently.
Investors hailed Monday's announcement with Fiat's share price rising 2.6 percent to €5.525, while the benchmark index was up 1.37 percent.