British Columbia Liberal leader Christy Clark said on Tuesday her party will implement a levy on thermal coal exports from the province if they are re-elected in a May 9 election and the federal government does not ban exports.

A re-elected B.C. Liberal government would develop regulations to levy a carbon price on all thermal coal shipped through B.C. ports to reflect the greenhouse gas emissions caused by its extraction, processing, transportation and combustion, she said in a statement.

Clark, whose Liberal party is trailing the opposition New Democratic Party in polls a week before the election, last week called on Canadian Prime Minister Justin Trudeau to ban thermal coal exports through British Columbia.

A coal levy, which would be the world's first greenhouse gas benchmark for thermal coal according to the Liberals, would make it uncompetitive to ship thermal coal through B.C. ports, Clark said.

The bulk of the coal shipped through B.C. is metallurgical, or steel-making coal, not thermal coal, which is used for heating. Some of the thermal coal that is exported through B.C. ports is shipped from coal mines in the United States.

B.C. environmental groups have called on the government for years to ban the export of thermal coal, saying it is a dirty source of energy.