OTTAWA (Reuters) -Canada could potentially use oil and gas exports as a lever in negotiations if U.S. tariffs on Canadian imports escalate, Foreign Minister Melanie Joly told a Toronto business audience on Wednesday.

Canada is vowing to impose tariffs on C$155 billion worth of U.S. imports but has so far not suggested it would either reduce exports of key commodities to the United States or impose tariffs on them.

Canada exports about 4 million barrels per day of oil to the United States, approximately 90% of its total crude exports.

"Of course, there’s oil and gas. We haven’t put that on the table yet, guys, we kept that in our game, in our cards, as cards that we could potentially play if this would escalate, and the U.S. knows that," Joly said.

Joly also said U.S. farmers would have to pay C$1.7 billion more if Ottawa imposed export tariffs on potash but did not specifically mention this as a potential card in negotiations.

Alberta, Canada’s main energy-exporting province, says it would never accept the idea of reducing energy exports to the United States.

Joly is a minister in the government of Prime Minister Justin Trudeau, who will step down after the ruling Liberal Party chooses a new leader on Sunday.

The two main contenders both say Canada should take a tough line with U.S. President Donald Trump over his tariffs.