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.