The board was recently increased to 15 from 11 members as part of the expansion.
"It could be maintained that . . . the unilateral change in the board's membership at this time is not reasonable and necessary to serve an important public interest," the memo reads.
Critics say the bill would set a precedent of political interference. The memo says the political appointments, without Rutgers' approval, could be unconstitutional.
A different Rutgers governing body, the board of trustees, ceded virtually all decision-making to the board of governors in 1956, the year the Legislature made Rutgers the state university of New Jersey. The board of governors has control over issues including setting tuition and approving new programs. The board of trustees is largely advisory.
But the board of trustees has ultimate responsibility for Rutgers' assets from before 1956, including broad swaths of land and buildings. Trustees have the power to withdraw those properties, which could cripple the university, as a last resort to preserve "Rutgers' self-governance." The memo includes a reminder of that power.
It also warns that the 1956 law may require the governing boards' consent to alter their structure because it was a contract between the board of trustees and the Legislature.
At a legislative hearing last week, Senate Minority Leader Thomas H. Kean Jr. (R. Union), who opposes adding appointees, asked Sweeney: "How in the world is this at all constitutional?"
Sweeney said he did not know, but added: "We'll see what happens in court."
Sweeney declined to comment Wednesday. He said last week that he had not commissioned a legal opinion but had spoken with lawyers who supported the legality of his bill.
The bill has been scheduled for a full Senate vote Thursday. Its corresponding bill in the Assembly also is scheduled to be heard Thursday by the Budget Committee.
Inquirer staff writer Andrew Seidman contributed to this article.