Q: Are presidential signing statements unconstitutional?
A: Probably not. But they don’t have much impact, either.
The use of presidential signing statements, which are official pronouncements made by the chief executive when signing a piece of legislation, dates back to the early 19th century. In more recent years, Ronald Reagan was an enthusiast and began making them on a regular basis. Subsequent presidents have followed his lead to a greater or lesser degree, with both Bill Clinton and George W. Bush being avid producers of these edicts.
Usually a signing statement contains some objection to the underlying law and announces that the law will be implemented according to the president’s interpretation of his own powers – which might conflict with statutory language. Some of Bush’s signing statements have objected to portions of various laws calling for the executive branch to provide lawmakers with information and reports so that Congress can perform its oversight function. Others have objected to laws that he perceives as limits on his national security authority.
Are they constitutional? It appears so, although the Supreme Court has never directly ruled on the question. Article I of the Constitution says only that the president “shall sign” bills with which he agrees and shall return measures he vetoes to Capitol Hill “with his Objections.” In other words, there’s nothing that requires the president to comment when he signs a bill, but nothing that forbids him from doing so.
But signing statements appear to have had little significant impact, at least when it comes to court rulings. The courts, which often take into account statements made by members of Congress when deciding cases involving statutory interpretation, have not given similar weight to presidential signing statements.
— Viveca Novak
Halstead, T.J. "Presidential Signing Statements: Constitutional and Institutional Implications." CRS Report for Congress, 17 Sept. 2007.
Savage, Charlie. "Examples of the President’s Signing Statements." The Boston Globe, 30 Apr. 2006.