Lindsay Lohan's father Michael is convinced his daughter is drinking again - and is blaming her rumored girlfriend Samantha Ronson for leading her astray.

The Mean Girls star checked into rehab last year following a spate of drink-driving offences, but has recently been spotted back on the Los Angeles party scene with DJ Ronson.

Lohan's father has now launched a scathing attack on Ronson, accusing her of corrupting his daughter and insisting the actress isn't working because she is always out partying with her pal.

He tells MSNBC.com, "It's (got) to the point now that I'm going to confront Samantha and Jenny Muro (Lindsay's production assistant) myself."

"Samantha drinks and passes the drinks under the table to Lindsay, and behind the scenes it gets worse and worse. Sam is using my daughter."

"My daughter isn't working because she's always with Sam. Even my ex-wife knows it. She just isn't doing anything about it."

A representative for Lohan has dismissed the claims, saying, "This is totally a lie and untrue."