Democratic Assemblyman Ted Lieu said he feared copycat fans might buy the machine for home use, which doctors say could harm a fetus.
"If someone sees Tom Cruise buy one, they think this is the thing to do," said Lieu. His bill, scheduled for debate Thursday in the California Assembly, would ban manufacturers in the state from selling, leasing or distributing the imaging device to anyone but a licensed medical professional.
"There's really no medical reason for an untrained person to use this machine," he said.
The actor's publicist, Paul Bloch, did not return phone messages seeking comment. Cruise has been promoting his new film, which opens in theaters Friday.
Doctors and technologists receive years of training to perform ultrasound exams, which offer parents the first glimpse of the fetus and obstetricians images to check a baby's health.
The machine is also used by doctors on a high-frequency setting to get a better snapshot of an adult's kidneys, pelvis, uterus and other internal organs.
There are many settings "you would only use on adults and not on a fetus," said Dr. Miyuki Murphy, director of ultrasound at Radiological Associates of Sacramento.
"Obviously, somebody enamored with their own child would want to use it all the time," said Murphy, identified by the California Medical Association as an expert on the topic. "You might push that button because the pictures are prettier."
One such device was listed Wednesday on the online auction site eBay and was selling for $5,500.
Critics of the bill said lawmakers should leave such decisions to health professionals.
"We don't have the expertise to dispense medical advice," said Assemblywoman Audra Strickland, the mother of a 6-month-old daughter.
The Food and Drug Administration has determined that "keepsake" fetal videos and personal snapshots are an unapproved use of a medical device.