This doesn't mean Ball's takeover of Rexam can't go ahead, but the US company will have to come up with some concessions to appease the antitrust regulator. It's likely the two firms will have to shed some of their assets in overlapping markets such as Europe and the USA.
"It is the view of Ball that the concerns raised ... allow the parties to develop the appropriate and adequate remedy package to bring about the successful clearance by the EU's competition authority of this proposed acquisition," the company said in a statement.
Read more: Can you believe it? Rexam share price jumps
Ball still expects that all necessary regulatory clearances will be obtained, enabling the proposed acquisition to close during the first half of 2016.
Ball now have until 9 December to address the Commission's concerns.
Rexam's board recommended the takeover by US can maker in February, and the Commission opened an in-depth probe five months later.
Rexam shares were trading up 1.8 per cent to 533p per share in London this afternoon.