Producers called paramedics to the starlet's hotel room last Friday when she wasn't responding to knocks on the door. Lohan's publicist said the 25-year-old was just napping after working long hours, and suffered exhaustion and dehydration.
Later, Lohan, who plays legendary actress Elizabeth Taylor in the Lifetime film, tweeted that she had worked 85 hours in four days.
Now, the Screen Actors Guild-American Federation of Television and Radio Artists is closely monitoring working conditions on the set.
Larry A. Thompson, the film's producer, said a SAG-AFTRA representative was on the set Tuesday and found no workplace violations.
In a statement, Thompson said the SAG-AFTRA representative "was totally fine with everything" she found during shooting at a Los Angeles estate. He was told there had been no complaints from guild members and that the visit was prompted by "tweets and comments in the media," he said.
The union said it will continue to pay visits to the set to enforce guild rules.
"We have spoken with representatives from the company, and they are fully aware of their contractual obligations. We will ensure that all applicable penalties will be paid," the guild said in a statement.
"Liz & Dick" is expected to wrap principal photography at the end of June after about four weeks of shooting in Southern California. The Lifetime Original Movie is based on the story of Taylor's torrid romance with actor Richard Burton, played by Grant Bowler.
The Associated Press contributed to this report.