Labour MPs' efforts to make the provision of "high-quality face-to- face careers advice" compulsory to all pupils and students in schools and colleges have failed.
Shadow ministers lodged an amendment to the Education Bill on Wednesday to secure changes to the Government's reforms, but it was voted down.
From next April, schools and colleges will not have the funding for such advice and neither will they have any legal obligation to provide it. Experts have warned that this will lead to provision being severely cut back.
The Government plans to set up a National Careers Service from this September, which would only give face-to-face advice to adults, not children.
Shadow education secretary Andy Burnham was behind the amendment and attempted to get it adopted by encouraging Liberal Democrat MPs to back him.
He was supported by the Association of School and College Leaders (ASCL) and careers adviser representatives. ASCL general secretary Brian Lightman said he was "extremely worried" by the Government's proposals.
"It's absolutely essential there is a service for children where they can get face-to-face advice given by qualified professionals, and this needs to be properly funded," he said. "At the moment it appears all the evidence suggests the new service will not be funded. Unless the Government ensures high-quality guidance is available for all young people, its social mobility strategy will be at risk."
Steve Higginbotham, president of the Institute of Career Guidance, said the passage of the bill through Parliament should be delayed to allow for more "coherent" changes.
"The Government should be brave enough to take a step back and give this bill more time, so we can have sensible dialogue," he said.
"They need to model how it's going to work, they need to consult with schools. Funding should be made available to ensure young people get a proper service.
"As it stands, these changes mean a young person will not be able to get careers advice unless schools pay for it. It's not a coherent national service, it's going to be fragmented and we are going to have a postcode lottery."