Sinn Féin leader Mary Lou McDonald has said her party would spend €3.8 billion on once-off measures in the forthcoming Budget.
She told her party think-in that such an intervention was extraordinary but necessary.
Sinn Féin says it would cap energy bills until the end of February by subventing energy companies at a cost of €1.6 billion.
The party is also calling for a windfall tax on excessive profits along with tiered cash payments for individuals rising to €500 for those on lowest incomes.
Ms McDonald rejected a suggestion from the Taoiseach that a cap on bills would take time to implement.
She said it must be prioritised and she said it can be done quickly.
"We saw in the Covid emergency that when the State and the State apparatus had to move quickly, it could move quickly so this is a question of political will," she said.
She said the Government's proposed energy credits could be swallowed up by future hikes in bills.
Capping bills would cut costs to consumers and also bring certainty at a time of soaring bills, she added.
TDs and Senators gathered at the Epic Museum in Dublin's docklands for a one day think-in ahead of the return of the Dáil tomorrow.
Speaking on RTÉ's Morning Ireland, Ms McDonald said her party is in favour of "a system of direct cash payments to households, but that would be in a targeted way".
Ms McDonald said it would not be a flat payment but rather a tiered system.
Sinn Féin leader Mary Lou McDonald has said an energy price cap is "essential" in order to provide affordability and certainty for households.— RTÉ News (@rtenews) September 13, 2022
She said this should be matched with a windfall tax on energy companies | Read more political coverage: https://t.co/jZge7My7C8 pic.twitter.com/0QYEc8R2cA
"A subvention of that scale and an intervention of this nature is absolutely proportionate and absolutely necessary given the unprecedented rise in energy costs," she said.
She said her party wants reliefs given by Government for diesel and petrol to continue and called for the removal of excise on solid fuel.
The winter fuel payment should also be enhanced and extended, she said.
Ms McDonald said Sinn Féin is concerned that the storage of liquefied natural gas would lock the country into fossil fuel reliance for the medium and long term.
"The truth is that we need to accelerate and unblock many of the processes that have held up renewables, particularly offshore," she added.
She said her party will publish its proposals in full on Friday.
On inheritance tax, finance spokesperson Pearse Doherty said his party believes the tax-free threshold for children should drop to €300,000 from its current level of €335,000.
However, he said the rate should rise from 33% to 36%.
It has been reported that the Commission on Tax and Welfare is advising that the threshold should drop closer to €32,500 over time.
Both Fianna Fáil and Fine Gael have voiced opposition to such a move.