It thus appears that anyone who has worked for the EU Commission risks their pension if they dare criticise it.
Lord Mandelson is entitled to the cash because he was the EU's trade commissioner from November 2004 to the middle of last year.
Under the terms of the deal, he will receive an index-linked pension of £31,000 a year when he turns 65. The cost of buying such a deal on the private market would be £550,000.
This is in addition to more than £234,000 of "top-up" salary payments and a £15,000 resettlement fee which he will receive over the next three years.
However, European Union rules show that if he speaks out against Europe as a former Commissioner he could be stripped of his pension altogether.
Documents seen by campaigners show that Lord Mandelson and other Commissioners have to abide by certain obligations "both during and after their term of office".
One of these obligations as a staff member of the Commission is to maintain a "duty of loyalty to the Communities".
The rules also note that "an official has the right to freedom of expression, with due respect to the principles of loyalty and impartiality".
If they fail to demonstrate loyalty to the EU, Lord Mandelson can be "deprived of his right to a pension or other benefits", the rules say.
The TaxPayers' Alliance, the campaign group that has uncovered the threat to his pension, said Lord Mandelson had to resolve this "conflict of interest".