When American watchdogs come to call, quoted companies take heed in a way that they might not with lesser regulators.

That NYSE Euronext, the stock and derivatives exchange, has launched an investigation into the trading of ABN Amro shares may not come as a surprise, but it will nevertheless put the Dutch bank on red alert.

The NYSE is interested in any potentially suspicious trading of American Depositary Receipts (ADRs) in the days before its agreed deal with Barclays was announced on March 19.

If it finds evidence to suggest insider trading, it will pass the matter on to the Securities and Exchange Commission (SEC).

This would mean that three sets of regulators would be looking into trading in the bank's shares: the Dutch AFM and the UK's Financial Services Authority are thought to be making inquiries of their own, although, as is customary, neither would confirm its interest.

Questions will be asked about whether any shares were traded using inside knowledge of events.

Were any of the numerous investment bankers involved indiscreet, for example, or did certain well-connected hedge funds find themselves in the know?

Although there is no suggestion that it was anything other than a victim, ABN Amro will be particularly keen to co-operate.

It has been on the wrong side of regulators before.

In December 2005, the bank acknowledged "serious mistakes" in its compliance with US anti-money-laundering procedures.

It was fined $75 million and served with a "cease and desist" order by five US authorities after its employees were found to have processed payments to outlawed countries, specifically Libya and Iran.

Whatever the outcome of the drawn-out bid battle that surrounds it, ABN Amro must ensure that it keeps the SEC onside.

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