Sean Penn directed the film Into The Wild

Last year Sean Penn flouted Ontario's laws by smoking at a press conference to promote All The King's Men, trade paper Hollywood Reporter said.

Public health officials went on to fine the Sutton Place Hotel, which hosts the festival's news conferences.

The annual event, now in its 32nd year, opens on Thursday with a gala screening of Canadian drama Fugitive Pieces.

The festival, regarded as one of the most important in North America, runs until 15 September.

Warning letter

Penn will be at the festival to promote his latest movie Into the Wild, which stars Vince Vaughn and Emile Hirsch.

The Sutton Place Hotel was fined last year for failing to post proper signage warning Penn and others that smoking is forbidden in public spaces in the Canadian province.

Ahead of this year's festival, Ontario's Ministry of Health Promotion sent a letter to Toronto organisers warning that no-one, movie stars or otherwise, can light up.

"The SFOA (Smoke-Free Ontario Act) requires proprietors and employers to ensure the public is aware of the prohibition on smoking, post appropriate signage as prescribed by the legislation, and ensure no person smokes in prohibited areas," the letter to festival organizers read.

"Non-compliance with these obligations could result in charges being laid."

In a statement festival organisers said they would abide by the province's no-smoking rules.

"We are aware of the Smoke-Free Ontario Act and will do everything in our power to uphold this law," the statement read.