The UK Border Agency (UKBA) has been asked by a Tory MP to investigate whether Ed Miliband's American campaigning guru is working illegally in the UK.
Labour has insisted veteran community organiser Arnie Graf has the correct visa for his activities and is not paid for his work, but have acknowledged he is reimbursed for expenses and loss of earnings during his visits to the UK.
Tory MP Priti Patel has written to the UKBA to investigate whether the payments breach the terms of his business visa.
Labour stressed that Mr Graf was not employed by the party and did not live in the UK, but only visited "a couple of times a year".
A Labour Party spokesman said: "Arnie Graf has a visa which allows him to enter the UK for permitted business activities. These activities have been fully disclosed to the UK immigration authorities when obtaining the visa .
"He is not employed by the Labour Party but advises us on campaigns and we reimburse him for lost earnings and expenses."
But Ms Patel has written to David Wood, UKBA's d irector general of immigration and enforcement, demanding an investigation into Mr Graf's status.
She wrote: " I am writing to ask the UK Border Agency to urgently investigate the case of Mr Arnie Graf, who I believe may be working in the UK illegally.
"According to The Sun newspaper, Mr Graf advises the Labour Party on campaigning, and visits the UK on a business visa. Mr Graf is also quoted as saying that he works with Ed Miliband.
"The Labour Party are on record as stating that they 'reimburse him for lost earnings and expenses'. I believe that this reimbursement for lost earnings constitutes Mr Graf taking paid employment, and would ask that you investigate whether this breaches the terms of his visa.
"Mr Graf has also appeared in a Labour Party video aimed at recruiting volunteers, I believe that this may constitute 'producing goods or providing services...directly to members of the public'.
"I am also concerned by the length of time that Mr Graf appears to have spent in the UK. It was reported in January 2011 that Mr Graf would be coming to the UK to advise Ed Miliband on the Labour Party's structure. According to UKBA's guidance, a business visitor must not visit for more than six months.
"Given that he reportedly continues to advise and regularly meet Mr Miliband, I believe that this would breach the legal requirement that business visitors do not intend to 'live in the UK for extended periods through frequent or successive visits'.
"As you know, paying individuals to work in the UK who do not have the appropriate visa is a serious criminal offence. I understand that the individual involved would also be liable for deportation. I would therefore be very grateful if you could investigate this case as a matter of urgency."