A High Court challenge against compulsory retirement at 65 was rejected today.
But charities for the elderly which launched the case vowed to take their battle to Parliament.
Age Concern and Help the Aged said the Government had only avoided defeat because ministers had already caved in to pressure for a review next year.
And Mr Justice Blake, who ruled on the case, said: "I cannot presently see how 65 could remain as a DRA (Default Retirement Age) after the review."
The two charities, now merged as Age UK, had argued that the Default Retirement Age introduced by the Government in 2006 is unlawful because it does not comply with an EU Directive against age discrimination.
But the Government argued that the EU directive on equal treatment in employment permits member states to allow differences in treatment on the grounds of age if they are objectively and reasonably justified by a legitimate aim.
Under UK law, a British employer can dismiss a member of staff without redundancy payments on their 65th birthday.
Employees do have the right to request working beyond retirement age, but although employers have a duty to consider these requests, they need offer no justification for refusal.
The charity said the High Court ruling was a blow for older people who need to work longer to secure a decent retirement in the face of recession and a drop in returns on savings and investments.
Following the ruling, Age Concern and Help the Aged challenged MPs to demonstrate their support for older workers by acting urgently to overturn the "outdated" legislation.
Andrew Harrop, head of public policy at Age Concern and Help the Aged, said: "Today's ruling does not spell the end of our campaign to win justice for older workers.
"In fact, we will be stepping up our fight to get this outdated legislation off the statute book.
"Despite the judgment today, ministers still have the opportunity this side of a crucial General Election to give real help to people in their 60s by outlawing forced retirement.
"They should amend the Equality Bill which is currently making its way through Parliament.
"In his ruling the judge makes it clear that the only reason he has allowed the law to stand is because ministers have already caved in to our pressure for a review of the law.
"He makes it clear that forced retirement at 65 is unsustainable.
"This judgment makes it crystal clear that this unfair legislation is past its sell by date."Reuse content