Alliance leader David Ford has accused Tony Blair of defying the Good Friday Agreement by failing to form a new executive without Sinn Fein.
David Ford wants an executive without Sinn Fein
Speaking at the party's conference in County Antrim, Mr Ford asked: "When will the government stop punishing every party for the defaults of one?"
He accused the prime minister of sacrificing integrity for inclusivity.
"Why is principle sacrificed to expediency time after time, when it just results in repeated failure?"
Mr Ford told the conference in Templepatrick that the Agreement lays out clear sanctions "against parties and individuals defaulting on their obligations to end violence".
He said devolution had to return to Northern Ireland so its politicians could tackle a range of problems for their constituents, but called for a voluntary rather than enforced coalition.
He again attacked the system of designating assembly members as unionist, nationalist or other, claiming it had only served to reinforce divisions and discriminated against cross-community parties like Alliance.
Earlier, the party's deputy leader Seamus Close said Sinn Fein had "poisoned, polluted and perverted the democratic process".
Speaking ahead of the conference Mr Ford criticised the government for withholding funding for an integrated school in Ballycastle.
"They seem prepared to say that if there are difficulties about resources, they will support division at the expense of integration," he said.
"I think that's a fundamentally misconceived view."