Australia on Monday finalised a long-awaited package of regulations for its domestic gas market as it aims to force down wholesale prices without choking off new investment in one of world's largest liquefied natural gas (LNG) exporters.

The mandatory code of conduct includes a A$12 ($7.98) per gigajoule cap on wholesale prices, first introduced in December, and mechanisms to make the quantity of gas produced more transparent and give gas buyers more leverage during negotiations.

But after months of lobbying from gas producers who warned the code would crimp investment, the rules include price cap exemptions for small, domestically focused producers. The energy minister will also have the power to exempt other producers for a variety of reasons, including new investment or supply deals.

Producers have already offered domestic supply commitments of at least 260 petajoules out to 2027, according to a government statement on Monday.

The rules put "government at the centre of the gas market" and make it responsible for any future shortfalls, the Australia Petroleum Production & Exploration Association (APPEA) said in a statement.

"Investment in new gas supply is now urgently needed to avoid shortages," APPEA CEO Samantha McCulloch said. "The government has taken the reins of the east coast gas market and with this comes the responsibility for ensuring sufficient supply and investment certainty."

The rules, which take effect on Tuesday, will only apply to new wholesale contracts in the physically interconnected east coast gas market. Australia's competition watchdog will enforce the code and review it every two years. ($1 = 1.5044 Australian dollars) (Reporting by Lewis Jackson; Editing by Jamie Freed)