The controversial pact with the Northern Irish Democratic Unionist Party comes after Ms May ended up losing her parliamentary majority in an election earlier this month that she had called to boost her support for Brexit talks.
Nigel Dodds, the Democratic Unionist Party Parliament member, charged the Labour Party with "hypocrisy of the highest order", claiming that it discussed with the DUP possible deals in 2010 and 2015, reported The Guardian.
In a statement read to the press, the former First Minister of Northern Ireland Ms Foster said: "Today we have reached an agreement with the Conservative Party on support for Government in parliament".
Liberal Democrat leader Tim Farron labelled the Tory-DUP arrangement as a "shoddy little deal", adding: 'While our schools are crumbling and our NHS is in crisis, Theresa May chooses to throw cash at 10 MPs in a grubby attempt to keep her Cabinet squatting in Number 10'.
"Where is the money for the Tory-DUP deal coming from?" the Labour leader asked.
The deal includes an extra £1 billion in public spending for Northern Ireland over two years.
The Defence Secretary has defended a £1.5bn deal with the DUP amid a mounting backlash, saying it will protect the Government from being "ambushed" on Brexit and other big issues.
She downplayed policy differences between her party and the more socially conservative DUP, which opposes abortion and same-sex marriage but the complicated process of removing Britain from the European Union.
Welsh first minister Carwyn Jones accused the Prime Minister was "ignoring the rest of the UK" by allying with the Northern Irish Party.
Sinn Féin President Gerry Adams said that powersharing at Stormont is the only fair way to distribute money from the DUP's deal with the Conservatives.
Mundell said last week that any funding for Northern Ireland should adhere to rules about funding for Wales and Scotland too.
Speaking in Downing Street, Foster said the government would channel an extra £1bn to Northern Ireland over the next two years.
Irish Foreign Minister Simon Coveney was in Belfast Monday as part of negotiations aimed at restoring a power-sharing alliance between the DUP and Sinn Fein almost four months after local elections in Northern Ireland.
The parties recognised the importance of the agricultural sector of Northern Ireland in the signed agreement.
"That is the terminology in which both parties will be addressing each other", said the source.
McDowell was part of a group of church leaders who are urging Northern Ireland's politicians to strike a power sharing deal for the common good of everyone.
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