A market analyst sent warning signals over the lack of clarity of the Federal Government's proposed resources rent tax, which is bringing uncertainty in the share market.

On Wednesday, the Government has declared that one of the biggest oil and gas project in Australia may be included by the tax.

The North-West shelf project, located at West Australia's Pilbara region, has produced more than 40 per cent of Australia's oil and gas, being one of the largest supplier of domestic gas for more than two decades.

Woodside, the project owner, and other joint venture partners are currently in consultations with the government on how the tax will affect their operations.

Under the proposed tax, companies are obliged to pay 40 per cent on profits above six per cent threshold, although it may be lifted depending on the outcome of the negotiations between the resource companies and the government.

Heather Zampatti, an analyst, suggested that companies should verify which projects may be affected by the tax.

"I think it would be fair to say that the proposed resources tax had added another level of uncertainty to our markets.

"Until we get some clarity as to what is going to be included, how much they can write off, we will continue to have this uncertainty in the market."

Ms. Zampatti also warned that companies have no chance for planning their projects, fearing that they may not become economically viable.

"If they come up with a number that's economically not viable then they're unlikely to go ahead. And, of course, Australia competes in a world market too so if companies look at what the underlying cost regime is and if they can do something cheaper somewhere else that's where they'll go."

She also added the proposed tax will make companies face more difficulties to access overseas funds.

West Australian Premier Colin Barnett admitted he was not aware of the new tax that would hit the North West Shelf project.