The theme of Labour's annual conference in Manchester is "rebuilding Britain" and party leader Ed Miliband will deliver his keynote speech on Tuesday.
But union leaders clashed with the Labour leadership over its refusal to promise pay rises for public sector workers.
Len McCluskey, general secretary of Labour's biggest union donor Unite, warned that his members were "furious" with the Labour leadership's "crazy" policy of supporting pay restraint
And Paul Kenny, general secretary of the GMB union, said Labour was "losing ground with core supporters by continuing to ignore the fact that millions of people are suffering".
In an interview yesterday, Mr Miliband conceded Labour still had "a huge mountain to climb".