U.S. lawmakers said Monday that they want to know how the Syrian government obtained American-made technology used to conduct online surveillance and block access to the Internet.

The Washington Post reported last month that the government of President Bashar al-Assad was believed to be using technology developed by California-based Blue Coat Systems in its bid to quash dissent in Syria. In a separate report, Bloomberg News reported that technology from another California company, NetApp, was being used by Assad’s government to monitor Syrians’ online activities.

In a letter to Secretary of State Hillary Rodham Clinton and Commerce Secretary John Bryson, three senators urged the administration to investigate whether the firms had provided “tools of repression” to Damascus.

“The sale of U.S.-made equipment that may have contributed to ongoing violence is unacceptable and should be investigated as soon as possible,” reads the letter from Sens. Mark Kirk (R-Ill.), Robert Casey (D-Penn.) and Christopher Coons (D-Del.).

The companies that made the technology have denied wrongdoing and said they also want to know how the Syrians got hold of their products.

Blue Coat has said it is aware that its products have been used in Syria but said that they were transferred there illegally by a distribution partner.

NetApp has said that it complies with U.S. export control and economic sanction laws, although it acknowledged that those controls could have been “improperly circumvented” without the company’s knowledge.

At a congressional hearing last week, a senior State Department official told Casey said the Commerce Department was looking into the Blue Coat report.

“Since the expert controls were put in place in 2004, any such item like this that would be exported to Syria, requires a case-by-case examination and an export license,” said Jeffrey Feltman, assistant secretary of state for Near Eastern affairs. “There was no — there were no export licenses issued for this.”

A spokesman for the Commerce Department did not immediately respond to a request for comment.

In their letter, the senators said they were concerned that, in light of the allegations, the U.S. government continues to do business with NetApp, noting that the firm signed a contract with the State Department as late as mid-September.

They called for the department to “immediately review the possibility of suspending all U.S. government contracts with NetApp until a full government investigation” is complete.