The US has launched investigations into Harvard and Yale universities over suspicions they received undisclosed funds from foreign countries, including Saudi Arabia and China.
The US Department of Education said the elite schools did not fully report hundreds of millions of dollars in foreign gifts and contracts.
Speaking to the BBC Harvard and Yale said they were preparing responses for the government. It comes amid a clamp down on foreign funding to academic institutions.
Under US law, universities are required to report all gifts and contracts from foreign sources that exceed $250,000 (£193,000).
Since July, the Department of Education said it had uncovered some $6.6bn in previously unreported gifts from countries including Qatar, China, Saudi Arabia and the United Arab Emirates.
Officials have previously described foreign spending on US universities as a "black hole" and warned that such money can come with strings attached.
The Department of Education said Yale University had chosen not to report any foreign funding over the last four years, and is suspected of failing to disclose at least $375m in foreign gifts and contracts.
The agency said it was also concerned that Harvard lacked "appropriate institutional controls over foreign money" and had failed to fully report foreign gifts and contracts.