One Direction fans rushed to the boy band's defence after footage was published appearing to show two of them smoking cannabis.
The video, on the Mail Online website, appears to have been filmed by Louis Tomlinson during their tour in Peru and seems to show him sharing a joint with bandmate Zayn Malik.
Louis can be clearly heard saying: "So here we are, leaving Peru. Joint lit. Happy days!"
At one point smoke is seen being blown across the car
A motorcycle police officer drives past and Louis says: "He's having a look. He's thinking 'I'm sure I can smell an illegal substance in there'. And he's hit the nail on the head."
Louis and Zayn are also heard joking about "illegal substances" as they smoke in the back of a car.
The pair also discuss One Direction's last book, with Zayn describing it as "so girly and not cool".
A spokesman for the band, who start the mainland UK leg of their Where We Are world tour in Sunderland tonight (May 28), said: "This matter is in the hands of our lawyers."
Thousands of fans took to Twitter to defend the band with one who tweets as voguemalik saying: "Zayn and Louis are both in their 20s. They are old enough to take care of themselves and do what they want."
Another fan, called cuddleharold, said: "Smoking weed doesn't make you a bad person but the media is gonna blow this up way out of proportion and I feel bad for Zayn and Louis."
The band, who have a huge following on social media, r ose to fame as teenagers on ITV's The X Factor talent show and have become one of Britain's biggest bands, with a huge and loyal following of young girls across the world.
Other band members Harry Styles, Liam Payne, and Niall Horan are believed to have been travelling in different cars and were not seen in the video.
Earlier this month, the band were named fourth in the Sunday Times Rich List of young musicians with an estimated fortune of £14 million each and a combined wealth of £70 million.
Ahead of the opening night of the UK leg of their Where We Are tour in Sunderland, fans who queued in heavy rain were keen to show their support for the band despite the cannabis allegation.
Outside the soaking Stadium of Light, where 52,000 screaming fans were due watch the show, Shelby Clark, 20, from Newcastle, said: "They could be doing worse, it's not that bad."
Her friend, Samantha Stirling, also 20 and from Newcastle, said: "At the end of the day, they are just young lads.
"I know it's prohibited but they are under so much stress.
"It doesn't put us off - we wouldn't be here if it did."
Tamsin Thompson, 13, from Peterlee, County Durham, did not believe the allegations, saying: "It's not true, it's fake.
"It's not put me off."
Deborah Pearson, from Chester-le-Street, County Durham, dismissed the drug allegation, saying: "That's life. They are just young lads."
Her friend, Lynne Laidler, said: "They are still good lads."