The new policy is in keeping with current prohibitions against smoking tobacco products on MTS vehicles or facilities.
"The popularity of electronic cigarettes has grown significantly in recent years," MTS Chief Executive Paul Jablonski said. "We now have uniform policy between the way we treat traditional cigarettes and electronic cigarettes."
The ban will go into effect July 18. The agency said fines will be $50 for the first offense, $75 for the second offense and $100 for subsequent offenses.
The amended ordinance prohibits passengers that "smoke or carry a lighted or smoldering pipe, cigar, cigarette, or tobacco or use any electronic smoking product or device that causes smoke, mist or vapor in any form."
The North County Transit District has a similar prohibition, as do many transit agencies across the state. The city and county of San Diego also have amended their codes to treat vapor inhalers like traditional cigarettes.
E-cigarettes have become popular as an alternative to smoking tobacco products, but concerns have been raised about health risks, particularly for nearby people impacted by secondhand fumes.