Below is an extract taken from the ATO website:
On 1 July 2012, changes were made to the tax and superannuation laws to reduce the scope for companies avoiding liabilities and payments of employee entitlements.
About the letter
Commencing in late April 2013, the ATO will be sending letters to directors of companies that have unpaid pay as you go (PAYG) withholding amounts. Some of these directors may be your clients.
The letter explains the director’s obligations and personal risk in relation to their company’s PAYG withholding debt.
It encourages directors to ensure their company addresses the outstanding PAYG withholding debt either by paying it immediately or establishing with us an agreed payment arrangement.
I am of the opinion that this will mark a steady increase in pressure to be applied by the ATO upon taxpaying businesses that have failed to remit tax as and when these obligations fall due. I suspect that activity regarding personal liability for directors where they fail to lodge within 90 days will be the next ‘cab off the rank’
Adrian Hunter 
Thanks Adrian
John Montgomery
Level 13, 189 Kent Street, Sydney NSW 2000
T: 02 9251 5222 I F: 02 9247 5911
E: JMontgomery@jonespartners.net.au
W: http://www.jonespartners.net.au