"Employers have no right to ask job applicants for their house keys or to read their diaries. Why should they be able to ask them for their Facebook passwords?" Schumer said in a press release sent to reporters.
Blumenthal said that by requiring job applicants to provide login credentials, employers could gain access to protected information that would be impermissible for them to consider when making hiring decisions. Those include religious affiliation and sexual orientation, which are protected categories under federal law.
Facebook said Friday that accessing such information also could open businesses up to discrimination lawsuits. The company said it might ask policy makers to take action to stop the practice.
"An investigation by the Department of Justice and Equal Employment Opportunity Commission will help remedy ongoing intrusions and coercive practices," Blumenthal said in the senators' statement.
Laura Sweeney, a Justice Department spokeswoman, said in an e-mail she had no immediate comment on the lawmakers' request.
Facebook and other sites are already used by some potential employers seeking additional background on job applicants because of the personal information posted there. As Facebook has given users additional ways to protect that information from public view, reports have surfaced of employers asking job applicants to voluntarily give them access by providing personal login credentials.
The Associated Press first reported the growth in the practice last week.
In a copy of the letter sent to Attorney General Eric Holder and provided to reporters, Blumenthal and Schumer asked the department to investigate whether the practice is a violation of the Computer Fraud and Abuse Act, the primary federal anti-hacking statute.
The lawmakers also asked the department to investigate whether the practice violates the Stored Communications Act, which prohibits intentional access to electronic information without authorization or in excess of authorization.
In a letter to EEOC chairman Jacqueline Berrien, the lawmakers requested an investigation into whether the practice "may be used to unlawfully discriminate against otherwise qualified applicants."
"We strongly urge the commission to investigate and issue a legal opinion," the letter said.