Fianna Fáil's Willie O'Dea has condemned the 2pc pay rise due to be paid to TDs from Thursday, around the same time some people's Covid-19 welfare payments are being cut.
Mr O'Dea and other key Fianna Fáil deputies have urged Public Expenditure Minister Michael McGrath not to implement the cuts.
Limerick City TD Mr O'Dea said the cutbacks were now a big issue in preparations for the Budget due to be presented on October 13.
"We should be cultivating social solidarity, but you can't do that if you're implementing really damaging cuts to people already on low incomes," Mr O'Dea told the Herald.
However, Mr McGrath app-eared unmoved by the stance being taken by Mr O'Dea, former agriculture minister Barry Cowen and dissident TD Jim O'Callaghan.
"I have to balance all the demands and be fair to all sectors, including other welfare recipients like people who were unemployed before Covid-19 and others such as carers," the minister told RTÉ.
Mr O'Dea has written to Mr McGrath, making the case against cuts to Pandemic Unemployment Payments (PUP) on grounds of fairness.
However, he also argued that it was important for keeping Fianna Fáil's identity in government.
Mr O'Dea has also condemned the 2pc pay rise that takes a TD's salary from €96,000 to €98,000. He said he will not take the increase, and revealed that he had refused an earlier rise too.
Separately, Laois-Offaly TD Mr Cowen's letter to Mr McGrath also criticised the failure of the Coalition to act on a raft of other health measures promised in the Programme for Government agreed last June.
Dublin Bay South TD Mr O'Callaghan said it was wrong of the Government to close businesses as a Covid-19 prevention measure without offering adequate income support.
Dublin Central Green Party TD Neasa Hourigan has also spoken out against the PUP cuts. It is not clear how many of her parliamentary party colleagues will take the same view.
Student leaders have warned against PUP cuts being applied to them as the payments to students are not a huge cost to the taxpayer.
Speaking to the Herald, Pádraic Toomey, president of NUI Galway students' union, said it would not be fair to cut students' PUPs.
Around 22pc had been in receipt of the PUP previously, so a high number of students had already been cut from the payments as they found jobs again when premises reopened.
"The nightclub industry has still not reopened and a lot of students are employed there, so to be targeting them is just unfair," Mr Toomey said.
"Until the full economy is opened up, including the night life, they can't be culling the payment when it's there to be used as a means to keep people going who are relying on it."