(ABC News) -- With millions purchasing protective eyewear ahead of the Aug. 21 solar eclipse, Amazon is working to remove potentially counterfeit glasses from its marketplace and issue refunds to those who have already bought them online.

A company spokesperson told ABC News in a statement overnight that it asked third-party sellers offering solar eclipse glasses to provide documentation to verify that their "products were compliant with relevant safety standards."

"The offers from sellers who provided this safety documentation remain available to customers," the spokesperson said.

Sellers who did not provide documentation for their listings have been removed from the site. Amazon did not name any of those listings or specific brands in its statement.

Amazon confirmed that it issued refunds to some customers who purchased glasses that may not meet industry standards.

Last week, Fred Espenak, retired NASA astrophysicist and photographer, told ABC News that he has heard rumors of counterfeit glasses being sold online.

Amazon says they have asked third-party sellers that were offering solar eclipse glasses to provide appropriate documentation to verify that 'their products were compliant with relevant safety standards.' (American Paper Optics)

Espenak, NASA and the American Astronomical Society (AAS) suggest that consumers purchase off the AAS's approved list of companies that manufacture and/or sell eclipse glasses and handheld solar viewers, which have been verified by an accredited testing laboratory to meet the ISO 12312-2 international safety standard.

"They've been put through a testing procedure to demonstrate that they're dark enough to prevent visible as well as ultraviolet and infrared light from passing through it," Espenak said.

Some companies are placing an ISO label on their counterfeit glasses, which is why following the list of manufacturers is a surefire way to know you're being safe, according to the AAS.

Here is a growing list from the AAS of approved companies that manufacture and/or sell glasses through vendors and retailers.

American Paper Optics (Eclipser) / EclipseGlasses.com / 3dglassesonline.com

APM Telescopes (Sunfilter Glasses)

Baader Planetarium (AstroSolar Silver/Gold Film)

Celestron (EclipSmart Glasses & Viewers)

Daylight Sky (plastic glasses only)

DayStar (Solar Glasses)

Explore Scientific (Solar Eclipse Sun Catcher Glasses)

Halo Solar Eclipse Spectacles

Lunt Solar Systems (SUNsafe SUNglasses)

Meade Instruments (EclipseView Glasses & Viewers)

Rainbow Symphony (Eclipse Shades)

Seymour Solar (Helios Glasses)

Thousand Oaks Optical (Silver-Black Polymer & SolarLite)

TSE 17 (Solar Filter Foil)