The ranking Democrat on the House Oversight Committee said it was "very difficult for me to sleep last night" after the director's testimony before the committee on Tuesday.
"I've come to the conclusion that my confidence and my trust in this director, Ms. Pierson, has eroded. And I do not feel comfortable with her in that position," he said on MSNBC.
That is a swing from just a day earlier, when he told reporters the "jury's still out" on her tenure.
His comments were even more blunt during a radio interview with Roland Martin on Wednesday.
"I think this lady has to go," Cummings reportedly said, referring to Pierson.
Cummings isn't the only lawmaker calling for Pierson to resign or be fired.
Rep. Jason Chaffetz (R-Utah) also said she should go in an interview with Fox on Tuesday night.
"I think it’s time that she be fired by the president of the United States or that she resign," he said.
Rep. Doug Collins (R-Ga.), a member of the Oversight Committee also called on Pierson to resign.
"I do not have confidence, especially given her answers of yesterday and the revelations of Atlanta, and then this continuing series of events, that it is probably best that she does step down," Collins said on MSNBC on Wednesday.
He also criticized Pierson over a press release she admitted approving that failed to disclose how far the intruder made it into the White House.
"I was appalled by her answer to that question," he said. "How could the director of the Secret Service approve a statement that was a lie?"
Rep. Gerry Connolly (D-Va.) said on MSNBC Tuesday that he is not ready to call for Pierson’s resignation, but called the Atlanta elevator incident "jaw-dropping."
"I want to give her an opportunity to complete her review and to provide, I hope, cogent recommendations for reform and corrective action,” he said. “But I have to say, it is an open question at the moment whether frankly she can continue in that job with any kind of competence.”
Pierson received a grilling on Capitol Hill over the security breach Sept. 19, when an intruder jumped the fence and made his way into the White House before being apprehended by agents.
New details emerged Monday about that incident. Cummings said those details have led to an erosion of public confidence in the director.
"No matter how wonderful Ms. Pierson may be, the public's confidence is eroding," he said on MSNBC. "There used to be a time where, if you thought about the Secret Service, you not dare do anything that might even make them think about you harming the president."
Other news emerged after the hearing, including reports that an armed security contractor with a criminal record was allowed on an elevator with Obama during a Sept. 16 trip to the Centers for Disease Control and Prevention.
Cummings said it seems the public is learning new stories about the Secret Service every week.
Cummings had expressed concern during the hearing that agents felt more comfortable talking to members of Congress rather than to their superiors.
"That has got to change," he said at the time.
Lawmakers on both sides of the aisle have called for an independent investigation into the events surrounding the incident. Cummings and committee Chairman Darrell Issa (R-Calif.) are expected to ask the Department of Homeland Security to investigate.
UPDATE: 10:55 a.m.:
Cummings tweeted Wednesday morning that he has not decided about Pierson, but he is "not comfortable" with Obama's safety.
I have not decided about Pierson, but I'm not comfortable about the safety of the President of the United States of America. #SecretService— Elijah E. Cummings (@RepCummings) October 1, 2014
In a later interview with NPR, the congressman said he has not made a final decision on whether the director should resign. He is expected to talk with Pierson by phone later in the day.
This story was last updated at 12:37 p.m.