The 26-year-old singer stars in the Hugo Boss ads with Victoria's Secret model Stella Maxwell but Liam admitted his mum Karen was not impressed when she first saw the sexy shots.
He told The Sun newspaper's Bizarre column: "Quite a few mates said they had to spin their cars around to try and get pictures of me across a bus — but it was my mum's reaction I remember best.
"She saw the shots just before they came out and obviously there's some very raunchy ones of me and Stella — so I tried to show my dad first to soften the blow.
"But she came back and saw what I was showing him. She was like, ‘What's that?' and saw Stella draped across me in this picture and then she hit me around the earhole. It took me right back to my childhood straight away."
Meanwhile, Liam - who is completely naked in some of the shots from the campaign - previously admitted the shoot was "basically soft-core porn".
He said: "There was a lot of tequila involved for this shoot. It just ended up being a lot more naked than I thought it was – and for [Stella] as well. She was also naked.
"And I was just, you know, 'Don’t look!' She was naked behind me and I was thinking, 'Liam, don’t look whatever you do.'
"There was a real hollow moment afterwards where I was sitting outside smoking cigarette thinking, 'I have basically just shot soft-core porn'.
"I don’t know how far this is going to go… That was just the first shot!"