President Barack Obama warned Congress this afternoon that he considers numerous provisions of the megabus spending bill to be unconstitutional, including provisions relating to detainees held at Guantánamo Bay, Cuba.

“My Administration has repeatedly communicated my objections to these provisions, including my view that they could, under certain circumstances, violate constitutional separation of powers principles,” Obama wrote in a signing statement today as he departed for his family vacation in Hawaii. “In approving this bill, I reiterate the objections my Administration has raised regarding these provisions, my intent to interpret and apply them in a manner that avoids constitutional conflicts, and the promise that my Administration will continue to work towards their repeal.”

Obama also said several other provisions interfere with his constitutional authority, including a provision requiring him to notify Congress of military exercises costing more than $100,000, as well as a limitation on placing U.S. soldiers in United Nations peacekeeping roles under a foreign commander.

“I will apply these provisions in a manner consistent with my constitutional authority as Commander in Chief,” Obama wrote.

Several other provisions involving foreign relations and related to Obama’s own advisers also will be effectively ignored.

Obama also wrote that “numerous provisions” in the bill condition the authority of the executive branch to spend or reallocate funds based on the approval of Congressional committees.

“These are constitutionally impermissible forms of congressional aggrandizement in the execution of the laws,” Obama wrote. “Although my Administration will notify the relevant committees before taking the specified actions, and will accord the recommendations of such committees appropriate and serious consideration, our spending decisions shall not be treated as dependent on the approval of congressional committees.”

Obama’s critics have said that by issuing signing statements at all, the president is violating a campaign pledge not to do so. “We’re not going to use signing statements as a way of doing an end run around Congress,” Obama said in May 2008, for example. But the White House has been firm since he took office that Obama never entirely ruled out using this tactic.