US President Barack Obama wooed working-class voters in his Labour Day speech on Monday, as Vice-President Joe Biden was urged to stand for the top job.

Mr Obama denounced Republicans for their “constant attack on working Americans” and said he was using his executive power to force federal contractors to give paid sick leave to their employees.

He was met with resounding applause at a major trade union rally and breakfast in Boston when he said he had signed the executive order aboard presidential jet Air Force One as he flew in to mark the US national holiday.

Roughly 44 million US private-sector workers do not receive paid sick leave, the administration said.

Mr Obama said that Republicans claiming to speak for US workers “have to walk the walk.

“You just wait. You look up at the sky and prosperity will come raining down on us from the top of whatever high-rise in New York City,” he said sarcastically. “But that’s not how the economy works.”

He added that the Republican mindset had been “wrecking the economy for a long, long time.”

In a reference to Wisconsin Governor Scott Walker, he remarked that one Republican candidate had “said busting unions prepared him to fight Isil,” an acronym for Islamic State.

Meanwhile, Mr Biden was greeted with chants of “Run, Biden, run,” at a march of union federation AFL-CIO in the city of Pittsburg — referring to his ongoing deliberations about whether to seek the Democratic Party’s nomination for next year’s presidential election.

With liberal warmonger Hilary Clinton trailing leftwinger Bernie Sanders in some polls, Mr Biden could be pushed as a union-friendly compromise candidate.

AFL-CIO president Richard Trumka introduced Mr Biden to the crowd as a “brother” and “a champion of working men and working women.”

Donning a black-and-gold United Steelworkers union hat, Mr Biden told hundreds of union members that the gap between the wealthy and poor was hurting US citizens.

“The tax code’s not fair. It’s simply not fair,” he said. “The wealthy aren’t paying their fair share. There used to be one America.”