The Senate’s own labor attorneys have been subpoenaed by a federal grand jury.

Sen. Charles Schumer (D-N.Y.) introduced a resolution Thursday to allow the Senate to pay for private attorneys for the chamber’s Chief Employment Counsel Jean Manning and Senior Chief Employment Counsel Erica Watkins.

Although the Senate’s own legal counsel would normally represent the two aides in the case, that office has demurred, citing a “potential conflict of interest” because of its “responsibilities” to the Senate Ethics Committee.

Schumer did not detail what information the subpoena seeks, only that both Manning and Watkins have been asked to give testimony and produce documents to a federal grand jury in Washington, D.C. He also did not offer any details about the potential conflict of interest.

The Senate Legal Counsel acts as the chamber’s attorney, representing Senators or aides in cases related to their official duties, as well as advising committees on subpoenas and investigations.

It is unclear how or why the Senate Legal Counsel is assisting the Ethics Committee, and the normally secretive panel rarely discusses its work. Both the Senate Ethics Committee and the Senate Legal Counsel declined to comment for this article but acknowledged the resolution approved by the Senate on Thursday.

According to a report issued by the Ethics Committee in January, at least four investigations remained open at the end of 2010.

In the only ongoing case it has publicly identified, the Ethics Committee has been investigating Sen. John Ensign (R-Nev.) since at least October 2009, and in February it announced it had hired a special counsel to take over the case.

The Ethics Committee has not identified the focus of its investigation, but Ensign has faced allegations that he tried to cover up an affair with the spouse of his former top aide. Ensign first acknowledged the affair with Cynthia Hampton, a campaign staff member married to Administrative Assistant Doug Hampton, in June 2009.

Ensign also faces questions over whether he helped Doug Hampton secure lobbying clients after he left the Senator’s office, potentially violating the Senate’s one-year revolving-door ban.

In the midst of that investigation, the Senate authorized a resolution to allow the Nevada lawmaker’s aides to testify before a federal grand jury investigating events surrounding Ensign’s affairs. According to a statement that Senate Majority Leader Harry Reid (D-Nev.) made in July, when the resolution was approved, that grand jury was also located in Washington, D.C.

The Justice Department declined in December to pursue allegations against Ensign in that matter; it is not known whether that investigation remains open regarding other matters in the Ensign case. It is also not clear whether Schumer’s resolution is related to the Ensign case.

The Hamptons’ attorney, Daniel Albregts, declined to comment for this article.

The Senate Rules and Administration Committee, which Schumer chairs, is charged with selecting and paying for the attorney to represent Watkins and Manning.

According to the Senate’s website, the chief employment counsel is tasked with providing “legal advice to, and represent[ing], Senate offices in employment law matters and lawsuits under the Congressional Accountability Act, which brings the Senate under eleven federal laws regulating the employer-employee relationship.”

Aides to neither Reid nor Schumer returned phone calls Friday inquiring about the subpoenas.