MPs will debate the Daylight Savings Bill today (Friday) which opponents warn could prevent people from attending morning services - especially in the north of England and Scotland.
Opponents say having an extra hour's darkness in winter mornings, to give an extra hour's daylight in the evening, will make it impossible to recite the morning prayers with a minyan before having to leave for work.
In winter, the earliest time for morning prayers is around seven am, but if the changes are made, it would mean eight o'clock in London and not until nine o'clock in the north.
Backers of Tory MP Rebecca Harris's Private Member's Bill argue that the change would save energy and prevent traffic accidents as children leave school.
The Board of Deputies said it was still consulting different communities before deciding whether formally to oppose the bill, with a decision "imminent".
Ephraim Borowski, president of the Scottish Council of Jewish Communities, said: "This change would make life very difficult for communities in Edinburgh and Glasgow. Shabbat would go out at quarter to one in the morning during summer. Michael Moore, Secretary of State for Scotland, has assured us he will oppose the change."
Chanoch Kesselman, of the Union of Orthodox Hebrew Congregations, said: "Many of the idea's supporters have no idea of its adverse effect on the Jewish community."
Ms Harris, MP for Castle Point, in Essex, said: "I hope employers would be sensitive to religious needs if the changes take place and that Orthodox people might realise that it might be worth compromising because of all the benefits extra sunlight would give to the whole country."