By Khanh Vu

HANOI, Feb 27 (Reuters) - Vietnam's Long Son Petrochemicals, a unit of Thailand's SCG Chemicals, is lobbying Vietnam to impose tariffs on imported polyethylene and polypropylene, as operations at its new $5.4 billion petrochemical complex remain suspended due to low margins.

"LSP is actively collaborating with relevant Vietnamese government agencies to expedite the proposal for applying tariff and non-tariff measures on PE and PP to protect domestic producers," the company told Reuters in an emailed statement late on Wednesday.

Polyethylene and polypropylene are raw materials that are used to make daily-use plastics such as bags and containers.

Last November, Siam Cement, Thailand's largest industrial conglomerate and owner of SCG Chemicals, suspended operations at the Long Son Petrochemicals complex after only one month due to "the chemicals' low margin".

LSP said it was focused on maintaining the facility, but said market conditions remained unfavourable.

"The petrochemical business situation is still in a low cycle amid a volatile global economy," it said. "Therefore, LSP is closely monitoring market conditions to make a prompt decision about resuming operations when the market becomes favorable."

LSP said it would invest $500 million to incorporate ethane as an additional feedstock for the complex, and expected the upgrade to be completed by 2027.

Companies are building more crackers in Asia to process U.S. ethane, which is cheaper than naphtha.

In its statement, LSP said it had signed a 15-year ethane supply agreement with an affiliate of U.S. gas supplier Enterprise Products Partners.

It said it had an agreement with Mitsui O.S.K. Lines for the long-term charter of three Very Large Ethane Carriers, and was seeking to secure another two charters of ethane carriers.

The LSP complex in southern Vietnam has annual capacity to produce 500,000 tons of high-density polyethylene, 500,000 tons of linear low-density polyethylene and 400,000 tons of polypropylene, using mostly naphtha and propane as raw materials imported from the Middle East.

(Reporting by Khanh Vu; Additional reporting by Florence Tan in Singhapore; Editing by John Mair)

((khanh.vu@thomsonreuters.com; +84 24 38259623;))