Muslim politicians from Labour and the Scottish National Party fear reduced voter turnout among Muslims on June 8, which falls during the holy month where fasting from dawn to sunset takes place.
Labour's Yasmin Qureshi, MP for Bolton South East, said: "It is unfortunate that Theresa May has scheduled the election to take place during the holy month of Ramadan.
"I know this will present challenges to Muslim voters and those who wish to campaign. At best I can only suggest that this did not even feature in her thinking, which is disappointing."
She added: "It may be that the election falling during Ramadan reduces turnout among Muslims."
And Rushanara Ali, Labour MP for Bethnal Green and Bow, said: "The fact that the general election will fall in the middle of Ramadan is not ideal.
"Holding an election during Ramadan means there could be a disproportionate effect on voter turnout in those constituencies with a sizeable Muslim population.
"If anyone thinks that their ability to go and vote will be affected, I urge them to register for a postal vote."
SNP MSP Humza Yousaf, the Scottish Government Minister for Transport and the Islands, also voiced fears that fewer Muslims will vote, adding that "you can never really hold an election at a perfect time".
"I think it would be fair to say that a lot of people in the Muslim community feel that they were certainly not even factored at all into the conversation or the thinking because it will have an impact, I suspect, on turnout," he said.
However, the Muslim Council of Britain said it could see "no reason" why holding the election during Ramadan - which this year is expected to be from around May 27 to June 24 - should have any impact on Muslims turning up to vote.
The group added: "There is probably more 'voter fatigue' generally across the country following the extensive recent campaigns in the lead-up to the 2015 general election and the 2016 EU Referendum.
"Muslims fasting during Ramadan will go about their normal daily activities and taking time out to cast a vote will have no impact on their choice to do so."
Sayed Yousif Al-Khoei OBE, chairman of the Al-Khoei Foundation, a Shi'a Muslim organisation, said: "In general, Ramadan and fasting is not supposed to impede normal life. It's supposed to be a spiritual experience.
"But for some people, you know, the combination of the hot weather... and lack of foods could be an impediment.
"But the spiritual uplifting of fasting should really make a Muslim more resilient and that should not really be a pretext for not voting, and I encourage everyone to use their right to vote."