In a letter to Apple CEO Tim Cook this week, the senators questioned the chief executive about a report from The New York Times in July that said Apple bowed to government pressure and removed apps that anonymize Chinese Internet users, allowing them to access an uncensored Internet. While the senators stopped short of accusing Apple of removing the apps, they expressed concern about the possibility of the company quelling access to free speech.

“If these reports are true, we are concerned that Apple may be enabling the Chinese government’s censorship and surveillance of the Internet,” the senators wrote. They went on to call China’s human rights record “abysmal” cited Reporters Without Borders, which has called China the “enemy of the Internet.”

“While Apple’s many contributions to the global exchange of information are admirable, removing VPN apps that allow individuals in China to evade the Great Firewall and access the internet privately does not enable people in China to ‘speak up’,” the senators wrote. “To the contrary, if Apple complies with such demands from the Chinese government it inhibits free expression for users across China.”

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Apple (AAPL) came under fire from free speech advocates over the summer after it pulled virtual private network, or VPN, apps from its Chinese App Store. The apps were designed to allow Chinese users to mask their identities and sidestep the “Great Firewall of China” to access sites banned by the government.

After the outcry, Cook confirmed in an earnings call with investors that Apple removed the apps, but he said that his company had no choice.

“We would obviously rather not remove the apps, but like we do in other countries, we follow the law wherever we do business,” Cook said on the call. “We strongly believe in participating in markets and bringing benefits to customers is the best interest of the folks there and in other countries as well.”

Cook went on to say that the “law is very clear” in China and required Apple to remove the apps. Cook added that Apple expressed its concern about the censorship “in the appropriate way” to the Chinese government.

In their letter, the senators asked Cook to answer a host of questions about the move, the company’s stance on censorship, and what Apple might have said in the past to the Chinese government about Internet freedom. They didn’t provide a deadline for answers.

Apple did not respond to a Fortune request for comment on the letter.