Stepping up a simmering constitutional conflict, House Speaker John A. Boehner warned President Obama on Tuesday that unless he gets authorization from Congress for his military deployment in Libya, he will be in violation of the War Powers Resolution.

In a letter sent Tuesday afternoon, Mr. Boehner, the top Republican in the constitutional chain of succession, said Mr. Obama must provide a clear justification by Friday for committing troops to Libya.

Sunday marks the 90th day since the president notified Congress that U.S. troops had been committed to help enforce a no-fly zone over Libya, which is designed to protect the rebels fighting Col. Moammar Gadhafi’s government.

“The Constitution requires the president to ‘take care that the laws be faithfully executed,’ and one of those laws is the War Powers Resolution, which requires an approving action by Congress or withdrawal within 90 days from the notification of a military operation,” Mr. Boehner said in the letter.