Washington, D.C. – Sources say that Democratic Senator Robert Menendez is expected to be charged by federal prosecutors with using his Senate office to push business interests, belonging to a friend and donor, in exchange for gifts.

The FBI and prosecutors have spent years pursuing the New Jersey senator who has fought off investigations for years, and the Justice Department’s public integrity unit has set up a high-stakes battle between the two parties. However, according to people briefed on the case, plans have been discussed between Menendez’s attorneys and federal officials for the New Jersey Democrat to turn himself in before a planned court hearing on Thursday.

Both Menendez’s and the Justice Department’s representatives declined comment. The relationship between the senator and Salomon Melgen, a Florida ophthalmologist and a political supporter and friend of Menendez, is what the government’s case centers on. Apparently, both Melgen and his family have been very generous to a number of committees the senator is associated with, as well as to the senator himself.

The Justice Department’s ability to prosecute sitting lawmakers will be faced with a high-profile test in the form of the case. Interestingly, the Justice Department has already spawned a legal battle between Menendez’s attorneys and prosecutors over key evidence the government has gathered and whether that evidence is protected by the Constitution’s Speech and Debate clause.