The Labour Party's General Election policies could "crack the foundations of our economy", while Tory immigration plans risk creating a skills shortage, a business leader has warned.
Confederation of British Industry director-general Dame Carolyn Fairbairn said December's election is an "extraordinary" one for business, hailing 2020 as the most important year in a generation due to recent uncertainty over Brexit.
She said Jeremy Corbyn's nationalisation plans will "freeze investment", and called on him to work with business.
Dame Carolyn, speaking ahead of the CBI annual conference, was asked if Mr Corbyn was a "friend to business", and told Sky News' Sophy Ridge On Sunday: "We look at the policies on the table and we have real concerns that they are going to crack the foundations of our economy."
Labour has already announced plans including free full-fibre broadband for all, a boost to NHS spending and a minimum wage hike to £10 an hour.
With parts of BT to be taken into public ownership under the broadband plan, further nationalisation proposals are expected.
Referring to "bolt from the blue" nationalisation plans, specifically with BT, she said: "That will freeze investment. I have talked to businesses who are already sitting there thinking 'maybe we're next'.
"So we do say again to Labour – work with business, work out different answers to these problems. But this programme that is appearing to value none of the contribution that business makes will simply shut investment out of our country."
Commenting on the Conservative Party's immigration measures, she said: "When we hear talk about brightest and best, I think that is a worry. If you do want to build 200,000 houses a year, you don't just need the architects and the designers, you need the carpenters, you need the electricians, you need the labourers.
"We need people to come and help us renew our economy."
She added: "It's not just brightest and best, it's people at all skill levels across our economy that we need."
The Tories are pledging to get "overall migration down", and under a range of measures, the "vast majority" of migrants will need a job offer to come to the UK to work, regardless of where they are from in the world.
The party said there will be a small number of exceptions, including high-skilled scientists and those who want to come to the UK to start a business.
A "unanimous agreement" was reached by senior Labour figures on Saturday regarding the party's manifesto after immigration was anticipated to be one of the most difficult issues to agree on.
The details of the manifesto will not be revealed until Thursday, but asked if free movement will end when the UK leaves the EU, Mr Corbyn told The Andrew Marr Show on BBC One: "There will be a great deal of movement."
Commenting on the Prime Minister ruling out an extension to the transition period, Dame Carolyn said: "One of the things I think is really important to understand is that if you are in business, living through the last three years, these rolling cliff-edges of climbing up a mountain with stockpiling and then climbing down again, could not be more damaging."
She added: "Let's make sure that we don't end up with yet another cliff-edge, possibly in June, or possibly at the end of December.
"Because every time we do that we take investment away from our country."
Meanwhile, Mr Johnson has said that all Tory parliamentary candidates have vowed to vote for his Brexit deal if he wins a majority.
In an interview with the Sunday Telegraph, the Prime Minister said this pledge means that voters can be "100%" certain that a Conservative government will "unblock" Parliament and deliver Brexit.
And Foreign Secretary Dominic Raab said he does not think it is remotely likely that the UK will leave the EU without a deal.
Asked on Marr "could we leave without a deal?", Mr Raab said: "I think it's, no, it's not what we're, I don't think it's remotely likely."