Cuba is the featured nation at this year's Equality Forum, Philly's annual summit on LGBT issues.
But Mariela Castro, perhaps Cuban's preeminent activist when it comes to LGBT rights, is unable to participate after the U.S. Department of State denied her a visa to travel to Philadelphia.
"We were quite shocked," Equality Forum Executive Director Malcolm Lazin said on Thursday.
"We asked what was the reason and there was no reason provided."
He said his group reached out to a senior member of the state Congressional delegation, as well as a prominent American, who both also contacted the State Department to request a reversal or explanation, to no avail.
"You would expect, hopefully, a response, even if it was an ordinary citizen, but in this particular case, she's both the daughter of the Cuban president and also someone who, in her own right, is internationally respected," Lazin said.
Castro, who was slated to participate in panel discussion "Cuba: Featured Nation" and to receive the International Ally for LGBT Equality Award.
"She is internationally recognized for her efforts on behalf of HIV education and prevention, transgender rights and is responsible for getting the Cuban government to pay for reassignment surgery," Lazin said.
Castro is president of Cuba's National Center for Sex Education, which conducts AIDS prevention education and advocates for LGBT rights in a country historically characterized as homophobic.
"It does seem like there's a role reversal here," Lazin said.
"You would expect that it would be Cuba who would deny our folks the opportunity to visit whoever they want and to say whatever they want.
"We just had a major visit by Beyonce and Jay-Z. As far as I could tell, they were allowed to go wherever they wanted, they were allowed to say whatever they wanted. I'm unaware of Americans who travel to Cuba being muzzled, in terms of not being able to express their viewpoints, so it is very disappointing as an American citizen to see our country embrace a counter-democratic response."
"I think we're really at the epicenter of the LGBT civil rights movement," he said.
"My guess is when people look back at 2013, it will be the year they point to, in part, because of the Prop 8 case and the DOMA case, but also look at the remarkable changes that are happening within the Republican party, the Boy Scouts, sports – literally across the board. It's amazing what's occurring and so this summit helps to reflect that both nationally and also through its featured nation."
For a full list of this year's events, click here.