The Bishop of Stafford Rt Revd Geoff Annas, the Christian leader of the Liberal Democrats Tim Farron and the Christian lobby group CARE have all signed an open letter to The Times newspaper, as the bill has its second reading in the House of Lords today.
Gambling machines are known as fixed odds betting terminals (FOBTs) because they have in-built chances of success before a person plays, to make sure they're profitable.
Currently, a user can spend £100 in a single spin of a FOBT, however the bill being read for a second time in the Upper House today would restrict that to £2 a spin.
There have been concerns that the FOBTs encourage addiction to gambling and that they particularly target people in poorer areas who have less money to spend.
The alliance's letter said: "In January 2014, the prime minister acknowledged there was a problem and that action would be taken if there was evidence to justify doing so.
"Since then, the story of two tragic suicides linked to FOBTs have emerged, which might have been prevented had the government not delayed reducing the maximum stake.
"We urge ministers to give the bill their full support and take appropriate action to deal with the social and economic harms being caused by FOBTs."
Premier has contacted the government for a response.
