The organisers of a so-called "straight pride" parade in Boston have claimed to be victims of terrorism after receiving envelopes full of glitter.
Three members of Super Happy Fun America called the authorities over envelopes filled with a "granular substance".
The letters prompted a response from the FBI, three fire departments and the bomb squad.
The FBI is investigating but says there is no threat to public safety.
Super Happy Fun America's president, John Hugo, told NBC that what happened was "an act of domestic terrorism".
Samson Racioppi, another member, said he was "immediately alarmed" after shaking the letter and hearing a rattling inside.
Racioppi said he told the other members of the group and discovered that John Hugo and Mark Sahady, the vice president, had received similar letters.
Bomb disposal experts were sent to the Massachusetts towns of Woburn, Salisbury and Malden.
According to Lt. Robert Roy of the Salisbury Police Department, the substance in the envelopes was glitter.
But John Hugo says he wants to "see this person prosecuted .. even if it's just baby powder".
So-called glitter bombing - covering someone in glitter- has historically been used as a means of protest against those who oppose LGBT rights.
Politicians from the Republican Party such as former Presidential candidates Newt Gingrich and Mitt Romney have been glitter bombed in the past for their anti-LGBT views.
Super Happy Fun America call themselves "an advocacy group for straight rights," though members of the group have been found to have links to far-right and white nationalist groups.
The city of Boston approved a permit for the controversial Straight Pride event to be held on August 31, but the event still needs permission from the state police and licensing board.
The organisers say they are "inclusive of all, including LGBTQ people" and the event is just "about free speech".
"It's perfectly natural and normal to celebrate heterosexuality, and the parade is not being held at any expense to the LGBTQ movement," said Racioppi.