Issa abruptly adjourned a hearing of the House Oversight Committee on Wednesday. He instructed committee staff to turn off the microphone of the committee's top Democrat, Cummings.
The hearing was on the improper targeting of tea party groups by the Internal Revenue Service. Cummings was trying to say that Republicans have overblown the controversy.
"This evening, Chairman Issa telephoned me and apologized for his conduct, and I accepted his apology," Cummings said in a statement. "My sincere hope is that as we move forward, we will respect the opinions of all members of the committee, we will proceed in a deliberate and considered manner to obtain the facts, we will refrain from making accusations that have no basis in fact, and we will seek resolution rather than unnecessary conflict."
Aides to Issa did not immediately respond to an email sent late Thursday night seeking comment.
House Republicans had blocked an attempt by Democrats to chastise Issa for his conduct at the committee hearing. Ohio Democrat Marcia Fudge offered a resolution condemning Issa for his "offensive and disrespectful manner."
But the House voted 211-186 to block the resolution.