WWW- Lindsay Lohan’s hard-partying antics and recent bout of “heat exhaustion” has left one Hollywood big shot steamed, The Smoking Gun has learned.

In a blistering July 26 letter to the 20-year-old actress, James G. Robinson, who heads the L.A. firm producing Lohan’s current movie, calls her recent erratic behavior “discourteous, irresponsible and unprofessional.” Robinson, the 70-year-old chief executive of Morgan Creek Productions, writes that Lohan has “acted like a spoiled child and in doing so have alienated many of your co-workers and endangered the quality” of “Georgia Rule,” a movie now being filmed and which stars Lohan, Jane Fonda, and Felicity Huffman.

Robinson’s letter was delivered to Lohan at the Chateau Marmont hotel. A Morgan Creek official confirmed to TSG that the missive was sent to Lohan and her various representatives earlier this week. Robinson notes that while Lohan’s aides have chalked up her lateness and absences to illness, he is “well aware that your ongoing all night heavy partying is the real reason for your so called ‘exhaustion.'”

Noting that Morgan Creek refuses to “accept bogus excuses for your behavior,” Robinson warns Lohan that she will be held “personally accountable” for losses caused by her actions. Claiming that Lohan’s behavior has already “resulted in hundreds of thousands of dollars in damage,” Robinson hints at possible legal action against the actress unless she begins honoring her production commitments. He concludes, “I urge you to take this letter seriously and conduct yourself professionally.”