The Justice Department said on Friday that Google would be required to license the software, to continue to upgrade it and to establish firewalls to hide ITA clients' proprietary information.
This is needed because Google intends to launch a new service providing flight search results that would compete with online travel services, the department said in court papers.
Google, the world's No. 1 Internet search engine, said in July that it would buy ITA Software for $700 million in cash. The announcement sparked concerns that travel websites such as Kayak and TripAdvisor could be deprived of ITA's software.
Disputes between Google and the online travel websites -- for example over fees -- are to be submitted to arbitration, according to court documents released by the department.
Google shares were up 0.3 percent at $581.70 on the Nasdaq on Friday afternoon.
(Reporting by Diane Bartz and Jeremy Pelofsky; Editing by Lisa Von Ahn and Matthew Lewis)