In Europe and France, rejecting the EU Constitution would be bad news for the economy and investor confidence.
That is how European Commission President Jose Manuel Barroso sees it.
He has appealed to French voters to back the charter.
Their referendum on it comes on the last Sunday of this month.
Barroso was giving an interview on Europe 1 radio.
It was his first major intervention in France’s preparation campaign.
Four successive polls this week have put the “No” camp ahead.
Another senior EU official said a “No” vote could open the way to nationalism and protectionism.