The Jewish speakers of the House of Lords and Commons are trying to bring forward the time of a scheduled address by the Pope to Parliament in order to avoid a clash with the start of Yom Kippur.
Organisers of Benedict XVI's four-day state visit to Britain from September 16 to 19 have already rearranged the time of the meeting once after concerns that Jewish parliamentarians would be unable attend.
They have scheduled it to end at 6 pm – 56 minutes before the onset of the fast and the start of the Kol Nidre service.
But John Bercow, speaker of the Commons, and Baroness Hayman, speaker of the Lords - both of whom are Jewish - are urging an even earlier finish.
A spokesman for Mr Bercow said: "Originally, the event was due to start at 5pm and both the Speaker and Lord Speaker said this would cause a lot of difficulty and quite possibly offence or the accusation of insensitivity. Efforts are continuing to achieve more flexibility."
The Chief Rabbi, Lord Sacks, will be unable to attend the historic address at Westminster Hall before an expected audience of 1,800.
Instead, he will be present at a lecture due to be given by the Pope to around 100 interfaith leaders at St Mary's University in London in the morning on the same day.
A spokesman for Lord Sacks said that the Chief Rabbi "looks forward to welcoming his Holiness on behalf of the Jewish community" at the interfaith event.
"The timing of his address to both Houses of Parliament on the eve of Yom Kippur will prevent the Chief Rabbi and some Jewish MPs and peers from attending.
"However the Chief Rabbi understands the very tight scheduling and does not regard this as a slight on the Jewish community."
A spokesman for the Catholic Church said: "The need for people to prepare for Yom Kippur came up when organising the trip. Clearly, the Church would want to ensure any religious observances and the need for people to get away.
"The programme has been adjusted in accordance with requests from the parliamentary authorities, specifically the two speakers.
"Initially, we thought there was significant time for people to get back.
"The Foreign Office's protocol team spoke to their Vatican counterparts and we found extra time which hasn't been easy. Every effort has been made to ensure the speakers will be able to get back in time and the timetable has been adjusted accordingly."