MIAMI (AP) — The U.S. is locking up more illegal immigrants than ever and generating lucrative business for the nation’s largest prison companies.

An Associated Press review shows the private firms have spent more than $45 million lobbying lawmakers and contributing to campaigns over the last decade as their share of detention beds has jumped from 10 percent to nearly half.

READ MORE: ‘Intense’ Yellowjacket Activity Reported Around Sacramento Area, Vector Control Says

The cost to American taxpayers for locking up the 400,000 immigrants detained is on track to top $2 billion for this year. The companies are expecting their biggest profits in the next few years because the government plans new facilities.

READ MORE: 2 Juveniles Arrested After Mother, Son Found Critically Injured In Elverta

The expansion is expected to continue even as the nation has seen a drop in illegal immigration. Federal officials told the AP privatization isn’t necessarily cheaper.

MORE NEWS: Dispatch Audio Describes Chilling Details of Boys' Alleged Attack On Own Mother and Brother: 'He Wants To Turn Himself In'

Copyright 2012 The Associated Press.