Verizon agreed to pay $3.4 million as a penalty for the 911 outage that affected its California customers in April 2014.

According to the results of a U.S. Federal Communications Commission (FCC) investigation, the company failed to notify call centers at least two hours before the outage that affected not only its California customers but millions of people from other states as well. For about six hours last year, 750,000 California residents were unable to reach a 911 representative.

Other states affected by the 911 outage included California, Florida, Minnesota, North Carolina, Pennsylvania, South Carolina and Washington. More than six million emergency calls didn't reach the call centers, according to PCWorld.

Verizon agreed to pay the fine and comply with the recommendations of the federal agency.

"Americans must have confidence that they will be able to reach 911 in an emergency," FCC Chairman Tom Wheeler said in a statement. "We take seriously our obligation to ensure the nation's 911 systems function reliably. We will continue to work with providers to ensure that advances in 911 technologies lead to improved communications between citizens and first responders."

Last year's outage is not new to Verizon. In 2012, the FCC started reviewing reports from Northern Virginia customers who were also unable to call 911 after the June 29 storms. The company blamed the outage on the failure of two generators at an office in Arlington County, Washington Post reported.

The FCC is now requiring Verizon to have "a far-reaching compliance plan" to ensure that the same problem will not happen again.