Rules allowing MPs to jump queues for things like lifts and restaurants in the Houses of Parliament have been called "a throwback to feudal times".
Staff working here have been told to know their place: behind the MPs
The Commons authorities have told those working in Parliament that "staff and other users should be prepared to give way to Members when queuing".
Kevin Flack who represents 380 TGWU union members said: "What will they want us to do next? Doff our caps?"
MPs already have sole use of a number of restaurants and bars in Parliament.
But the e-mail tells those working in Parliament: "When using parliamentary facilities, please bear in mind whether there is, or is likely to be, a heavy demand from Members and, if so, try to amend your own plans or schedule."
Mr Flack said his members understood the need to give MPs priority at busy times - for instance, in the run-up to important Parliamentary votes.
But, he added: "I can't think of an occasion when an MP has been denied his fish and chips because of a huge queue of staff."
He said the irony was that most of the staff who were being told to give way were employed by the MPs themselves.
"It's not as if we are tourists - we are actually helping MPs do their jobs," he added.
Not all MPs appear to have welcomed the latest ruling, which covers places like staff canteens which are open to anyone working in the Palace of Westminster.
Liberal Democrat MP Lembit Opik has called on his fellow members to condemn the new rule, saying that it creates a "rigid two-tier system which is counter to an enlightened image of Parliament".
Lembit Opik: Opposes the change
He told BBC Radio 4's Today programme: "This will cause resentment. I suspect it's a cross-party initiative of the 'don't you know who I am' brigade.
"We don't really want those people to be in charge of throwing our erstwhile staff to the back of the queue."
Now the unions have invited the chairman of the committee that brought in the new rules to explain himself.
Labour MP Frank Doran has been summoned to a meeting in the House next Tuesday, where members of the Parliamentary T&G branch and the Secretaries and Assistants Council hope to learn the reasons behind the move.