The computer networks managing major natural-gas pipelines are currently experiencing a series of cyberattacks, according to government officials.
The attacks have been going on for months and involve fraudulent emails targeting employees of the gas companies.
He said the department's Industrial Control Systems Cyber Emergency Response Team began working with the gas companies in March to "prepare mitigation plans customized to their current network and security configurations to detect, mitigate and prevent such threats."
The Christian Science Monitor first reported on Friday that the Homeland Security Department had alerted gas pipeline companies about a coordinated effort to breach their systems.
The alert said the attacks were "related to a single campaign from a single source" and appear "to have started in late December 2011."
It is unclear how much damage, if any, the attacks have caused.
The incident comes as Congress is debating whether to require critical infrastructure, such as gas pipelines, to meet minimum cybersecurity standards.
Senate Democrats and the White House argue that minimum standards are necessary to protect critical systems from devastating attacks.
A gas pipeline accident in San Bruno, Calif., in 2010 caused a massive explosion that killed eight people and destroyed 38 homes. Supporters of the mandates argue that hackers could cause a similar catastrophe with a cyberattack.
But Republicans say the regulations are unnecessary and would burden businesses.
House GOP leaders have indicated they will not allow a floor vote on any legislation that creates new cybersecurity regulations. Last month, they passed their own cybersecurity bill, the Cyber Information Sharing and Protection Act (CISPA), that focuses only on voluntary information sharing and does not include mandates.
Democrats are currently revising their legislation to an attempt to secure the 60 votes needed to pass the Senate.
Caitlin Hayden, a spokeswoman for the White House National Security Council, said senior administration officials met with Senate staffers on Monday to brief them on the cyber threats facing critical infrastructure.
"The classified briefing is intended to provide staff with an appreciation for the cyber threat facing the nation as the Senate prepares to consider new legislative authorities that could help the U.S. Government prevent and more quickly respond to cyber intrusions and attacks," she said.