Don Cruickshank, chairman of the campaign, said any businesses in the telecommunications, energy, water and sewage sectors that failed to measure up would be among those exposed.
With 14 months to go, Mr Cruickshank said, the time for "generalisations" about such large and important companies was over. Action 2000 would concentrate its attention on "laggard" firms and sectors crucial to the economy.
But the least prepared in the business community are small and medium- sized enterprises, which employ one in three workers in the private sector and which face closure if their computer systems are unable to cope. Some systems will close on the stroke of midnight; others will misinterpret information.
While nearly nine out of ten big companies have tackled the problem or are on the way to dealing with it, only six out of ten firms employing between 10 and 250 people are in the same position.
Mr Cruickshank said smaller businesses had a responsibility to themselves and their employees to ensure they could cope. "Too many of these companies are playing a high-risk game with their business's profitability and reputation and their employees' future," he said. One in 12 of the larger companies say they will discriminate against suppliers who are not actively addressing the problem.
"I know that the general economic outlook is poor in many sectors, but this is not a good reason for knowingly and unnecessarily hammering yet another nail into their company's viability," said Mr Cruickshank. It was found that businesses in Wales, Northern Ireland and the West Midlands had the most ground to make up.
And among industrial sectors, construction, agriculture and road transport were the least prepared.
Giving a practical example of what might happen, Mr Cruickshank said a large supermarket might order fresh supplies through its usual electronic system, but find that the supplier misinterprets the order, erroneously reports that the goods are not available or is simply unable to receive it.
Officials at the campaign are "alarmed" by the number of companies that believe the whole problem has been exaggerated.