A directive issued by Premier Gladys Berejiklian last month informed the state's most famous cultural institutions the Waratah was to be "the only brand identity" used on all communications including advertising and signage.

That would involve ditching the distinctive logos used by government agencies, such as the Opera House, Taronga Zoo, Sydney Olympic Park, the Art Gallery of NSW, the Australian Museum and Barangaroo.

Senior current and former staff at the agencies privately indicated they were taken by surprise and were now scrambling to secure an exemption - with one suggesting it was "like an episode of Utopia", the ABC comedy series satirising government bureaucracy.

A Sydney Opera House spokeswoman confirmed the iconic destination was informed of the directive by email and was now urgently seeking an exemption, noting the strength of its existing logo and branding.

"The Opera House brand is itself a significant NSW government asset, and the Opera House has worked over many years to develop a strong brand with significant national and international reach," the spokeswoman said.

"How the Opera House uses its existing logo and branding will be subject to the government's decision."

A Sydney Olympic Park spokeswoman confirmed the organisation had also been hit by the directive and was in ongoing discussions with the Premier's department to seek an exemption. Taronga Zoo declined to comment.

The crackdown was issued on August 7 and, according to the government, was necessary to "ensure consistency across public sector communications and improve the recognition of NSW government projects".

It stipulates the Waratah must be used "prominently" on all advertising, project signage and external communications, and its to be the only such logo used. Previous exemptions to the rules would no longer apply.

The directive applies to all NSW government departments, state-owned corporations, statutory authorities, advisory entities, councils under the Local Government Act and universities, and compliance is "mandatory".

Ms Berejiklian's office referred inquiries to the Department of Premier and Cabinet. A spokesperson declined to answer specific questions but said exemptions were available "where there is a compelling reason to do so".

Exemptions can only be granted by a sub-committee of cabinet. Exempt agencies can be classed as "independents", such as courts, meaning they need only display their own logo - or as "co-branding identities".

Co-branding identities are required to display both their own logo and the Waratah, but the Waratah "must be the more dominant mark". "It should always be slightly taller," the guidelines stipulate, and must be placed "in the most visible and valuable space".

The NSW government spokesperson said the cost of the rebranding exercise would be "minimal" because the Waratah was an existing logo and agencies that adopted it could do so as part of their routine communications updates.

However, it is understood the exemption process has taken up significant time and resources for several cultural institutions.

Not all affected agencies were worried about the rebranding. One media manager told the Herald it was "not a big deal" and "these things happen in the public sector".