Flotilla organization.
Flotilla organization. IDF website

One of the main organizers of the “Freedom Flotilla 2” to Gaza is linked to the Al-Aqsa Foundation, which the U.S. Department of Treasury has designated as "a critical part of Hamas' terrorist support infrastructure."

Amin Abu Ibrahim, also known as Amin Abu Rashed, is one of the main organizers of the second flotilla to Gaza and a founder of the European Campaign to End the Siege of Gaza (ECESG), a central organization participating in the flotilla. 
Recently, the Dutch daily newspaper De Telegraaf cited Abu Rashed as the "brain behind the flotilla", and noted that according to a Dutch journalist who had spent time with the flotilla organizers, Abu Rashed's role as the flotilla's main backer was kept secret until the ships all arrived in Greece. 
Earlier this year, the Bethlehem-based Ma'an news agency referred to him simply as a "campaigner" in an article Abut the upcoming flotilla. Abu Rashed was an active participant in last year's flotilla as well. 
Why the secrecy? The IDF Blog reports that Abu Rashed’s name came up during the prosecution of the case against the Holy Land Foundation by the US government in 2007. 
The Holy Land Foundation is designated by the U.S. Treasury as a Specially Designated National and banned by the EU for its direct financial and material support to Hamas. During the Holy Land Foundation trial, a letter was shown written by Abu Rashed to Akram Mishaal, a director of the Holy Land Foundation and a cousin of Hamas leader Khalid Mashaal.
In the letter found at Holy Land Foundation headquarters and used as a court case exhibit by the U.S. government, Abu Rashed lists the names, addresses, and bank numbers of "charitable organizations working for Palestine in Europe." Abu Rashed was writing as a representative of the Al-Aqsa Foundation, an organization designated by the U.S. Department of Treasury as a charity financing terror and "a critical part of Hamas' terrorist support infrastructure."
These "charitable organizations" cited in Abu Rashed's document were also later declared by the U.S. Department of Treasury to be supporters of terrorist organizations, specifically Hamas, and consequently their assets were frozen.
Many Hamas affiliated organizations, as recognized by the U.S. Treasury, were organizations in which Amin Abu Rashed was “a very active participant in to say the least,” according to the IDF Blog. “Now, as leader of the current flotilla to Gaza, this raises deeper questions regarding the intentions of the flotilla organizers and their further connections to Hamas.”