FILE PHOTO - U.S. Senator Dean Heller (R-NV) arrives at the Senate Judiciary Committee Privacy, Technology and the Law Subcommittee hearing on Capitol Hill in Washington, DC, U.S. on November 13, 2013. REUTERS/Yuri Gripas/File Photo

(Reuters) - A threatening note was left over the weekend at the Las Vegas office of a Republican U.S. senator from Nevada who may cast a decisive vote over a healthcare bill aimed at dismantling Obamacare, police said on Monday.

Officers who responded to a burglary alarm at the building housing Senator Dean Heller’s office found the note near the office door on Sunday morning, the Las Vegas Metropolitan Police Department said in a statement.

The content of the note was not released and police are investigating. The alarm was triggered by motion sensors and there was no forced entry to the building or Heller’s office, spokesman Officer Larry Hadfield said by phone.

Heller, who is up for re-election next year, is under pressure over his potential vote on the revised bill before the Senate that would roll back the 2010 Affordable Care Act, former Democratic President Barack Obama’s signature domestic accomplishment, popularly known as Obamacare.

Heller is among a dozen Republican senators who have expressed reservations or remained noncommittal about the revised bill.

Republicans control the Senate by a 52-48 margin and cannot afford to lose more than two from within their ranks because of united Democratic opposition. Two Republicans have already said they oppose it. Senate Majority Leader Mitch McConnell has delayed a vote on a retooled bill.

Heller’s office declined to comment on the letter, citing an ongoing investigation.