It poses a dilemma for Mr Brown who has followed Tony Blair's lead of trying to keep business onside. Now may be the time to put the relationship at arm's length. What's good for business is not necessarily good for Britain.
It was important to the credibility of New Labour breaking from its unelectable leftist past that business approved. But the party is well beyond that now and, in this election, now clearly a choice between a bigger or smaller state Labour and business must part company.
Business leaders have allowed the Tories to portray them as speaking in the public interest. But that claim is not credible.
Business executives have a different agenda, outlook and approach to their jobs. They are there to cut costs, improve the bottom line and to grow their firms. The techniques they apply to achieve these goals – and incidentally make their fat cat bonuses – would lead to the break-down of public services if they were to be let loose in government. You'd get efficient but extremely limited services.
Just imagine how our National Health Service would look if Michael O'Leary, chief executive of super-efficient Ryanair were to head it up. Sure, he'd abolish queuing. It would a first-come-first served rush to casualty with the doors slamming shut 20 minutes before the surgery was due to close. He would, of course, offer Speedy Access at a small extra cost. But you'd have scramble for a seat on the ambulance.
Or how about putting Diageo's Paul Walsh – one of the signatories to the letter of support for the Tories – in charge of economic development? He's the guy who is shutting down the Johnny Walker plant in Kilmarnock after 190 years indifferent to the local misery it will cause. The broader picture doesn't interest him.
And quite rightly so. Business cannot be expected to be responsible for all of the social consequences of its action. That is the role of government. So take with a pinch of salt any business view on what taxes are better.
The number of businessmen opposing Labour's proposal for a increase in National Insurance contributions has been rising like the red line on a charity thermometer outside a church. But Labour should not pay a blind bit of attention to this view or any others on economic management that they will inevitably trot out before 6 May.
They are promoting their own narrow interests. It's not the effect on the national economy of a rise in NI contributions that worries them. It is the fact that this particular tax rise doesn't suit their businesses' agenda.
Of course, it's obvious that the more expensive labour is the fewer jobs will be on offer – if employment is, indeed, that sensitive to cost. Where the deception comes in is in that these business leaders failed to acknowledge that the alternative to this "tax on jobs" will be cuts in public expenditure leading to even greater jobs losses.
But they regard that as a positive. It is part of their philosophy to see a shift from public to private sector. And, of course, higher unemployment makes their recruiting easier and cheaper.
The key services that government has to protect – health and education – are the very ones our business leaders opt out of. They send their kids to private schools and their remuneration packages all include private health insurance. So when they offer their views on the reform of the NHS they are thinking of redesigning a system for the punters – not one they or their families will have to encounter except in theory.
Their concern is as personal as that for the quality of food in the staff canteen in their factory.
Business is no different from the trade unions in seeking to promote its own interests. But at least trade unions are pretty upfront that they are pushing particular policies because they are out to do the best for their members. One wonders where businessmen derive the arrogance to pontificate on matters of state as if the country's interest coincided with theirs.
Charan Gill, the Glasgow restaurateur, offered an interesting insight in a speech to the Entrepreneurial Exchange. He revealed that as a boy in India, the people who commanded respect and whose opinions were sought by the villagers were the rich and successful.
That, he said, was what motivated him to work so hard to establish his thriving empire.
He wanted his opinions to be listened to. And his assumption is one that society tends to make – that wealth and power bring knowledge and wisdom.
Many of our self-made businessmen, Labour supporter Alan Sugar for one, clearly believe it. Take his money but ignore his views. And at a local level, many councils seek the advice of their local business hero – like Glasgow's Willie Haughey, much in the papers recently – the doyen of enterprise initiatives. Though how being involved in a nightclub, running a pub and servicing supermarket fridges qualifies you to shape regeneration strategy has always escaped me.
Because the assumption isn't true. Success in business is no proxy for the ability to run a country.
Gordon Brown shouldn't be so mealy-mouthed in the face of this orchestrated attempt to undermine him. The next time they stick their heads above the hustings parapets he should turn the guns on them. There's plenty about Labour's record for business to criticise.
Equally, business has a lot of failings he could expose – lack of investment in the knowledge economy and in training and re-skilling, for example, despite government help. Labour has no need to try and placate these guys.
Remember, the last business leaders to command awe were our bankers. Now all they generate is shock.
Michael Kelly is a former Labour lord provost of Glasgow