The consumers watchdog goes to court in order to stop a unit of south-east Asia's biggest phone operator Singapore Telecommunications Limited from running misleading advertisements.

The Australian Competition and Consumer Commission (ACCC) filed a lawsuit with the Federal Court of Australia is also pushing for the unit, SingTel Optus Pty Limited, to advertise corrections and to pay fines.

In a media releseae, “the ACCC alleges that Optus engaged in misleading or deceptive conduct and made false representations in relation to the advertising of certain broadband plans as part of its 'Think Bigger' and 'Supersonic' promotional campaigns.”

The watchdog claims Optus' advertisements fail to inform customers of limitations on promised download speeds. In Optus' ''Think Bigger'' campaign, a 120-gigabyte speed for $49.99 ($45.50) a month. Download speeds were promised to be four times faster than the original plan in the ''Supersonic'' broadband campaign.

However, the ACCC disclosed that “once the customer exceeds the peak data allowance, the internet connection is limited to a speed of 64kbps.” The commission “alleges that Optus did not sufficiently or clearly disclose, and in some cases did not disclose at all, these qualifications.”

The case is on the Federal Court's Fast Track list. A hearing is scheduled for September 16.