But how employers are affected - and what they need to do - is less clear.

Under the scheme, the federal government will make a fortnightly payment of $1,500 to each eligible employee until 27 September 2020.

The money would come through the normal payroll system, just like wages before the big hit. The government pays the money to the employer who pays it to the employee.

Companies have to show that their incomes have been cut (or are going to be cut) substantially. Otherwise, it would amount to a tax-payers subsidy to companies which really don't need it.

Smaller businesses (with a turnover up to a billion dollars a year) have to show that their turnover has (or will have) dropped by at least 30 per cent compared with normal times.

Bigger businesses which take in at least a billion dollars have to show that that turnover has dropped (or will have dropped) by at least half.

It is not, according to Dr Steven Hamilton of the Tax and Transfer Policy Institute at the ANU.

The government fact sheet for employers says that to qualify a business would have to establish that it "has, or is likely to, face the relevant fall in their turnover".

They have to predict their fortunes.

But what if a business doesn't know what its turnover in the coming months is going to be (and who can predict the future in these unpredictable times?)

The government says: "There will be some tolerance where employers, in good faith, estimate a 30 per cent or more or 50 per cent or more fall in turnover but actually experience a slightly smaller fall."

But "some tolerance" hasn't been defined. Would companies have to repay the subsidy if their sales turned out to be better than expected, say because the virus crisis was resolved more quickly than expected?

All the indications are that the measure was worked out quickly (as perhaps it had to be in a fast-moving crisis).

The federal government went from opposition to a full embrace and announcement in a matter of days.

Dr Hamilton wonders if that has led to potential pit-falls and loopholes.

For example, might a company be tempted to reduce its income to get its turn-over down to just below the threshold for getting the subsidy?

The measure could have several unintended consequences, he said.

"For example, for Qantas the subsidy would be almost $600 million, but to receive it, its revenue will need to fall to 50 per cent below where it was this time last year. That might discourage it from reopening routes, which would slow the recovery.

"The scheme will also make it harder for businesses desperately in need of staff (such as supermarkets) to hire new workers from currently struggling businesses."

In general, workers on temporary visas are not eligible while permanent residents are. There's an exception for workers from New Zealand. Short-term casuals are not eligible, either, and the two groups combined make up about two million workers.

The payment of $1,500 a fortnight does not depend on an employee's income but it is not clear how the tax system would treat it. Much may depend on the employer.

Imagine an employee who in normal times earned $1,500 a fortnight. On that, he or she was taxed - an amount of tax was held back by the employer and paid to the Australian Tax Office.

If that employee now gets stood down but is paid the $1,500 JobKeeper allowance instead of his or her wage, will the employer still withhold tax?

The ATO says: "An employer must still withhold tax on the payment on behalf of the employee, and must still comply with their Pay As You Go withholding obligations."

Some companies may be eligible for the "Cash Flow Boost".

"If eligible, the employer will receive credits equivalent to the amount withheld from wages paid to employees in the March to June 2020 periods, up to a maximum of $50,000 for those periods.

"In practice, this means they keep the amounts they have withheld from payments for those periods, however, there are some exceptions, such as when the total withholding liability across those periods exceeds $50,000."

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We don't know. Payments will be back-dated to the announcement at the end of March but no date for payment has been announced. This means that some eligible businesses may have to find a way of paying bills in the uncertain meantime.

You can. The government says: "The JobKeeper Payment will support the income of sole traders and maintain connection with their employees. To support self-employed people, eligible businesses will be able to nominate one eligible person (such as an owner) to receive the JobKeeper Payment."

The same rules apply in terms of drop in turn-over as they do for bigger companies.

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