The justice department quietly added a provision barring the IRS from auditing Donald Trump’s tax returns on Tuesday, amending a widely criticized agreement that creates a secretive and loosely controlled $1.776bn fund to compensate allies of the president.

The addendum, signed by Todd Blanche, the acting attorney general, says the government is “forever barred” and “precluded” from examining the tax returns of Trump, his family, company and “related companies”. The agreement applies to anything filed before the agreement was reached. It was posted on the justice department website on Tuesday morning, a day after the department announced creation of the fund.

The inclusion only adds to mounting scrutiny of the wider agreement reached on Tuesday. The arrangement was announced after Trump said he was dropping a $10bn lawsuit against the IRS and other specious claims against the government in exchange for creating the compensation fund. IRS officials recommended fighting Trump’s lawsuit, the New York Times reported on Tuesday, but the agency decided to settle it anyway, raising further questions about improper interference.