Angela Rayner is expected to face off top British business chiefs in a co-ordinated attack to destroy her "deeply damaging" overhaul of workers' rights.
Since coming to power last July, the Deputy Prime Minister's colleagues have urged her to dilute the plans so that they become more palatable for industry leaders who have long-opposed her vision.
In an attempt to water down the plans, business bosses are drafting a joint letter to send to the House of Lords before a debate on the Employment Rights Bill is scheduled to take place next week.
In their General Election manifesto, Labour pledged a new flurry of laws would see the end of "exploitative" zero-hour contracts and assume flexible working to be the automatic "default" for everyone.
Business leaders have expressed their concerns that Rayner's radical plans will suffocate businesses and smother the industry in red tape
GETTY
Business leaders have expressed their concerns that Rayner's radical plans will suffocate businesses and smother the industry in red tape.
They also fear the overhaul will impede any attempt to combat the national benefits crisis - another issue which Labour has promised to tackle.
A draft of the letter to the Lords has warned of "grave unintended consequences" of giving workers further "day-one" rights while the Prime Minister is under pressure to increase living standards across Britain.
Rayner's bill is due to be scrutinised by the Lords this week and has just passed its third reading in the House of Commons.
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Under Labour's new plans, some of the new workers' rights will include a "day-one right to request flexible working".
The law will also grant employers the ability to take companies to court for "unfair dismissal" from the day they start the job, and grant a handful of new powers to the unions.
Written by the Confederation of British Industry (CBI), the letter chastises the decision to giving the employer the right to claim unfair dismissal, arguing that such a measure would make businesses "hamstrung".
The letter has also asserted that such a radical overhaul would allow the unions to "behave unreasonably".
It reads: "Our collective position is that, as currently drafted, the Bill will have deeply damaging implications for the Government’s priority growth mission but also their admirable focus on tackling rising economy inactivity and the growing number of young people currently classified as Neet.
"Taken together, that is a recipe for damaging, not raising, living standards."
The letter will be sent by the B5 - a group of business groups, including the British Chambers of Commerce, CBI, Federation of Small Businesses (FSB), Institute of Directors (IoD) and Make UK.
Under Labour's new plans, some of the new workers' rights will include a "day-one right to request flexible working"
PA
"Businesses will be forced to make difficult choices between jobs, investment and growth as the headroom for higher employment costs has already been more than taken up by the increases in employer NICs," it adds.
"In addition, there are key areas where the scope of the policy that will be enacted by the Bill goes far beyond the outcomes outlined in the Labour manifesto. As such, the risk of grave unintended consequences has been compounded rather than addressed," it reads.
The letter summarises: "Together, we are calling upon the Lords to fully scrutinise and improve this legislation in order to find a landing zone that is genuinely both pro-worker and pro-business."
A Government spokesman said: "Through our transformative Plan for Change, this Government has delivered the biggest upgrade to workers’ rights in a generation, and our measures already have strong support amongst business and the public.
"We’ve consulted extensively with business on our proposals, and we will engage on the implementation of legislation to ensure it works for employers and workers alike."
