Two letters addressing recent controversies touching both Massachusetts candidates for U.S. Senate pulled the campaign trail rhetoric deeper into issues of character Wednesday, adding new pressure for transparency from both candidates.

In one letter, U.S. Senator Scott Brown demanded Harvard Law School Professor Elizabeth Warren release a comprehensive list of corporate legal clients she counseled while at Harvard. Brown’s campaign then came under fire in a letter from Bill John Baker, the principal chief of the Cherokee Nation, denouncing two Brown staffers who were videotaped doing tomahawk chops and calling out war chants at a political rally earlier this week.

The letters point to what has increasingly become the contest’s dominant theme: character. Brown has raised various questions about Warren’s transparency in the past, specifically whether or not she benefited from her claims of Native American ancestry while at Harvard and the University of Pennsylvania.

The issue resurfaced quickly at last week’s senatorial debate, followed by new allegations by Brown that Warren fought against victims of asbestos exposure while representing Travelers Insurance. On Monday, Brown pointed to another case in which Warren helped LTV Steel avoid paying into a retirement fund for miners.

“In each case, your work for these corporations is at odds with the image you portray on the campaign trail fighting for the middle class and the little guy,” Brown wrote in his letter Wednesday.

Harvard Law School professors must report annually any outside work they take on. The Law School does not release this information.

Warren responded to Brown’s letter at a rally Wednesday morning, where she received the endorsement of the Professional Fire Fighters of Massachusetts.

“Since I went into public service in 2008 I have released all of my financial disclosure. I have released all of my client contacts. And I must say I’m a little surprised to hear this from Senator Brown. As I understand it, he has been in public service now for 25 years and has never released the name of a single client,” Warren said.

Released less than an hour later, Baker’s letter came in response to a video put online earlier this week that showed two Brown staffers performing a “tomahawk chop” and shouting mock war cries at a political rally. Baker said the incident “goes far beyond what is appropriate and proper in political discourse.”

“The use of stereotypical ‘war whoop chants’ and ‘tomahawk chops’ are offensive and downright racist,” Baker wrote. “A campaign that would allow and condone such offensive and racist behavior must be called to task for their actions.”

Brown said his campaign did not condone such action, but has yet to take any specific action on the incident.

—Staff writer Nicholas P. Fandos can be reached at nicholasfandos@college.harvard.edu.