Sen. Rand Paul (R-Ky.) wrote Senate colleagues on Tuesday expressing opposition to reauthorizing the Patriot Act.

Paul, a freshman GOP senator with who's seen as a figurehead of the conservative Tea party movement, urged colleagues to give serious pause before voting to reauthorize the Patriot Act, the antiterrorism law first passed in response to the 9/11 terrorist attacks.

"I call upon each of my Senate colleagues to seriously consider whether the time has come to re-evaluate many—if not all—provisions of the PATRIOT Act.  Our oath to uphold the Constitution demands it," Paul wrote in a "Dear Colleague" letter released Tuesday.

The House voted on Monday night to reauthorize most expiring provisions of the Patriot Act, the controversial legislation first authorized last decade that gives the government more expansive abilities to investigate suspected terrorists and acts of terrorism.

The reauthorization passed in a 275-144 vote after failing in a procedural vote requiring a supermajority last week. A number of freshman Republican lawmakers, some of whom were allied with the Tea Party movement, voted against reauthorization -- a move that took Republican leadership by surprise, and served notice of the GOP freshman class's independence.

Paul might look to sew similar seeds of discontent in the Senate, which now has to consider Patriot Act reauthorization. The Kentucky freshman said his main objection to the legislation centered around the authority it gives to the government to conduct warrantless searches or wiretaps in some situations.

"It is not acceptable to willfully ignore the most basic provisions of our Constitution—in this case—the Fourth and First Amendments—in the name of 'security,'" Paul wrote.