It's the first time the House of Bishops have issued such a letter.
It'll be revealed at 1pm but is expected to include thoughts on the benefit system, living wage and immigration.
Speaking on BBC4's Today programme, the Bishop of Buckingham, Dr Alan Wilson, who helped write the letter said: "We're not telling people how to vote but why to vote."
But Christian Tory MP Nadine Dorries has raised her concerns over the letter. She said: "The Church is always silent when people are seeking its voice and yet seems very keen to dive in on political issues when actually no-one is asking it to."
The letter comes after the Church faced a backlash from the government over perceived criticism in the Archbishop of York's book 'On Rock or Sand'.
In it Dr John Sentamu said the poor are being "left behind" and whole cities in the UK are being "cast aside". He later denied that his words were aimed at the current government.