HSBC has written to Muslim organisations across the UK to inform them that it is closing their bank accounts.
The letters say that continuing to provide services to them would be beyond the bank's “risk appetite”, and that it made the decision because it was "applying a programme of strategic assessments to all of its businesses".
Organisations affected by the decision include the think tank Cordoba Foundation and Finsbury Park Mosque in North London.
On 22 July, the treasurer of the mosque received a letter from HSBC saying that its account would be closed on 22 September.
Khalid Oumar, one of its trustees, told the BBC that he questioned the motives of the bank. "The letters that have been sent and the letters that we received do not give any reason why the accounts were closed in the first place," he said.
"That has led us to believe that the only reason this has happened is because of an Islamophobic campaign targeting Muslim charities in the UK."
Finsbury Park Mosque is one of the largest in London. It is also where Abu Hamza, the Muslim cleric who was recently convicted of 11 charges of terrorism in a US court, served as an imam.
The mosque's chairman, Mohammed Kozbar, stressed the extent of the challenges that it would face as a result of the closure. "They have put us now in a very, very difficult situation - this is the only account we have,” he said.
"For us it is astonishing - we are a charity operating in the UK, all our operations are here in the UK and we don't transfer any money out of the UK. All our operations are funded from funds within the UK."
He added that the move could have wider impacts on the Muslim community's relationship with HSBC: "We are sure that our community will be frustrated, and might consider closing their accounts themselves with HSBC if the bank doesn't reopen our account, or at least give us an explanation."
The bank has been accused of racial discrimination following the decision. In response, a spokesman for the bank said that the closures were “absolutely not based on race or religion”.
"Discrimination against customers on grounds of race or religion is immoral, unacceptable and illegal, and HSBC has comprehensive rules and policies in place to ensure race or religion are never factors in banking decisions," he said.
In 2012, the bank was fined $1.9bn (£1.2bn) by the US authorities after it was accused of helping to launder drug cartel money. It was the largest amount ever paid in such a case.