"Hunger striking" women at the Yarl's Wood immigration removal centre have been told by the Home Office their protest could lead to their deportation being speeded up.
The letter from a Home Office immigration enforcement manager at the centre told detainees refusing food or fluid "may, in fact lead to your case being accelerated and your removal from the UK taking place sooner".
After a visit to Yarl's Wood last month, shadow home secretary Diane Abbott said she was told by detainees that around 65 women were refusing food but management had denied it was a hunger strike.
Responding to the letter Labour MP David Lammy said he would be raising the "threats" at the centre in Bedfordshire - which was described as "a place of national concern" by the Chief Inspector of Prisons in 2015 - with ministers.
Mr Lammy tweeted: "I will be asking Home Office ministers to explain this and how these threats relate to due process, human rights and the treatment of human beings in a civilised society."
The letter, obtained by the Detained Voices website, also advises protesters that their refusal of food or fluid "will not lead to the progress of your immigration or asylum case being halted or delayed" and "will not lead to your removal directions being deferred".
They are being told their protest "will not lead to you being granted permission to stay in the UK" and "will not automatically lead to your release from detention".
It is understood that the Home Office sends such letters when it feels there is a need to ensure that a person who is refusing sustenance is doing so from an informed position and is aware of any impact it may or may not have on their case.
The Home Office said it only removes people with no legal right to remain in the UK and that protesting detainees are being closely monitored by healthcare professionals.
On February 23, when Ms Abbott visited Yarl's Wood, she raised concerns about standards of medical care, access to legal help and the length of detention faced by some of the women.
Last week, Tory frontbencher Baroness Williams of Trafford rejected the charge that people were held indefinitely, pointing out the majority of people were detained for no more than four months.
Some people may remain in detention longer because of launching appeals against their removal, she said.