The largest U.S.-based companies expanded their untaxed offshore stockpiles by $183 billion in the past year, increasing such holdings by 14.4 percent, according to data compiled by Bloomberg.

Microsoft Corp., Apple Inc. and Google Inc. each added to their non-U.S. holdings by more than 34 percent as they reaped the benefits of past maneuvers to earn and park profits in low-tax countries. Combined, those three companies alone plan to keep $134.5 billion outside the U.S. government's reach, more than double the $59.3 billion they held two years earlier.

The build-up of offshore profits — totaling $1.46 trillion for the 83 companies examined — is increasing because of incentives in the U.S. tax code for booking profits offshore and leaving them there. The stockpiles complicate attempts to overhaul the tax system as lawmakers look for ways to bring the money home and discourage profit shifting.