The petition drive was started last October by billionaire Tom Steyer and has, according to his Facebook page, five million signers nationwide.
Some of those have been Democratic U.S. Congress members including Arizona's District 3 Representative Raul Grijalva. However, Romero becomes the first local politician to sign it.
"I am not alone," Romero said. "There are people throughout the country, in this community, that believe Trump is unfit to be the President of this country."
While there was no specific tipping point, Romero cites a litany of issues including the Russian meddling in the 2016 election, multiple accusations by women of sexual harassment, and the recent allegations involving porn actress Stormy Daniels.
"The possibility of seeing an election in this year, 2018, being meddled with again and the Trump Administration not doing anything to protect our democracy, I can't sit and watch this happen." she said. "I'm deeply committed to my country, I'm deeply committed to democracy."
The Chair of the Pima County Republican Party, David Eppihimer, called her decision to sign the petition a "political stunt."
He called it "outrageous, almost humorous on some level" and that she's "just playing politics."
As for potential criticism, Romero says "I'm used to pushback, I'm used to people using my gender and my ethnicity against me."
The city attorney's office says Romero did not violate any city policy because the Twitter account is her own and is part of her campaign page. As part of city policy, it is not part of the public record.
She said today is about women's empowerment and recognizing that policies approved in Washington DC, oftentimes, have a negative impact on women.
Women tend to lag on wages, are impacted by climate change, social attitudes and harassment. Now is the time to acknowledge that and begin to work towards equality.
"Because it's Women's Day, I believe we shouldn't just say 'hey', send out Twitter and Facebook posts, and say congratulations, we actually have to do something about it," she said.