Plans to work round the clock on the Channel Tunnel Rail Link (CTRL) near King's Cross in north London have been rejected by a planning inspector.
Residents living near the site objected to noise, dust and traffic
The project, due to be completed in 2007, is behind schedule and developer Union Railways wanted to work 24 hours-a-day.
But people living next to the site on the Coopers Lane estate said it would have made their lives a misery.
CTRL says the decision will have "significant implications".
Work on the link is believed to be three months behind schedule.
The proposals had already been rejected by Camden Council but the company appealed against that decision leading to a two-day inquiry last month.
CTRL says if the deadline is missed it would mean millions of pounds lost in bonuses and penalties.
Reduced journey times
In a statement, it said: "This will have significant implications for the project programme as indicated in our evidence at the public inquiry and we will be looking carefully at the steps open to us."
When complete, the Channel Tunnel Rail Link will extend for 109km (68 miles) from the tunnel to St Pancras station via Stratford in east London.
The first 46-mile section to Fawkham Junction in north Kent was opened in September.
When the £5.2bn project is completed journey times from London to Paris will be reduced from two hours 40 minutes to two hours 15 minutes.