More than 100 business leaders have declared their support for the Conservatives, warning a "change of course" after the general election would "put the recovery at risk".
Senior executives from leading British companies - including five who have previously backed Labour - signed an open letter praising the Conservative's economic policies.
Labour dismissed the letter as "nothing new".
Labour leader Ed Miliband has pledged to prevent working people from exploitation by employers mis-using zero-hour contracts.
He said the battle lines had been drawn between his party, which he said would back working families, and the Tories, who he claimed were only looking after the country's elite few.
ITV News political correspondent Carl Dinnen reports:
More than 100 people claiming to represent working people across Britain have signed a letter backing Labour in the general election.
Tories take campaign to the factories of three businesses who publicly endorsed their economic plans.
Read the letter carefully, don't worry, it's short. Note that while it praises the Conservative-led government it does not mention Labour.