The FTC added that it will refer two executive officials from the companies to the prosecution for further investigation.
They are accused of colluding to raise prices of 5-6 mm plate glass products used for construction four times from November 2006 to April 2009. The product prices were allegedly raised by about 10-15 percent each time.
They were found to have fixed prices through phone calls and offline meetings, and raised product prices in different timing in order to avoid suspicion from authorities, the FTC said.
The price hikes were shifted to the prices of apartment buildings that used the materials, eventually causing damage to many home purchasers, according to the corporate watchdog.
The two companies were fined in 1997 on similar charges.