Church Action for Tax Justice has questioned Prime Minister Boris Johnson's pledge to raise the higher tax threshold from £50,000 to £80,000 at a time when more people across Britain are turning to food banks to ensure they have enough to eat.
Mr Johnson made the promise in his first speech as Prime Minister this week in which he also pledged to put 20,000 more police officers on the street by 2022, and increase funding for primary and secondary schools across England.
In addition to raising the higher tax band, he also suggested that corporation tax could be cut, although he did not specificy by how much.
Dr Justin Thacker, the group's national coordinator, warned in a letter to Mr Johnson that while the changes would benefit the wealthy, they would result in less money being available to fund vital public services.
He said it was important that the Government seek ways to end the growing reliance on food banks across the UK, many of which are run by churches.
"We think tax regimes should be fair, transparent and serve not just the present but also future generations, not just the wealthy but especially those who are poor," he said.
"We are therefore concerned about your reported plans to reduce taxes for those who earn the most. We urge you to think again, ensuring first that the public purse is able to support public services in such a way that we see an end to the growing use of foodbanks, many of which are run by churches."
Dr Thacker called on Mr Johnson to ensure that corporations are held to account and pay their fair share of tax in order to contribute to public services.
He said that for this to happen, the Government needed to close down the legal loopholes that make tax dodging possible.
"You can drive the legislative agenda that will bring about the change you have indicated," he said.
"As I am sure you are aware, it has been estimated that the UK loses up to £90bn per year through a range of tax avoidance and evasion measures.
"That money could easily pay for the improvements in public services that you have promised from greater funding for the NHS to more bobbies on the streets.
"At the start of your premiership then, we urge you to begin the process of closing the loopholes that enable so much tax to be dodged."
The Government has pledged to publish the registers of public ownership in the UK's crown dependencies and overseas territories by 2023. While Dr Thacker welcomed the move, he said it should be done sooner.
"The great British public pay their taxes, and we are sure they would appreciate it if, as Prime Minister, you ensured the wealthy, both individual and corporate do so as well," he said.
