A bipartisan group of ethics advocates lobbed a second letter to President-elect Donald Trump on Monday evening warning him that he needs to do more to separate himself from his family business interests.

The letter comes after Trump announced some changes in his business empire, with more expected before Inauguration Day.

The letter signers include two conservative allies of Trump senior adviser Stephen K. Bannon — Peter Schweizer, the author of the book “Clinton Cash,” which outlined possible conflicts of interest posed by Hillary Clinton because of donations to her husband's charitable foundation, as well as John Pudner, who went to high school with Bannon and now runs the advocacy group Take Back Our Republic.

Monday's letter urged the incoming president “to divest your business enterprises into a true blind trust managed by an independent trustee having no family relationship with you, or the equivalent, in accordance with the guidelines of the Ethics in Government Act.”

The letter expressed appreciation for the steps that have been taken by Trump to address his conflicts of interest problems, including terminating or limiting plans for Trump projects in Brazil, Azerbaijan, Georgia and elsewhere and shutting the president-elect's charitable foundation.

But the ethics experts said more action is required: “As long as you continue to maintain ownership of The Trump Organization, no other steps that you take will prevent the serious conflicts of interest, appearance of conflicts, and Emoluments Clause problems that will exist throughout your presidency. In these circumstances, you cannot separate the presidency  from your business enterprises.”

As President-elect Donald Trump prepares to take office, questions and concerns have been raised over how his business interests may interfere with the business of running the country. The Washington Post spoke to Public Citizen to untangle and unpack the potential consequences of Trump's conflicts. (Alice Li/The Washington Post)

The 29 signers to the letter included Republicans and Democrats, and liberal and conservative groups. In addition to Schweizer and Pudner, signers include Norm Eisen, President Obama’s chief ethics lawyer, and Richard Painter, former president George W. Bush’s chief ethics lawyer. They also include two former Republican governors and five former Republican House members.

The signers conclude with a tough warning: “Respectfully, you cannot serve the country as president and also own a world-wide business enterprise, without seriously damaging the presidency.”

--Rosalind S. Helderman contributed to this report.