The roster of celebrities includes British and American actors Susan Sarandon, Mark Ruffalo, Gael Garcia Bernal, Peter Capaldi, Maxine Peake, Viggo Mortensen, Steve Coogan, Charles Dance and Harriet Walter.
The letter, organised by Artists for Palestine UK, reads: "We join Emma Watson in support of the simple statement that ‘solidarity is a verb’, including meaningful solidarity with Palestinians struggling for their human rights under international law. We oppose injustice anywhere in the world and stand with all those seeking an end to oppression."
Artists for Palestine UK launched in 2015, and describes itself as "a growing network of artists and cultural workers standing together for Palestinian rights and for a just resolution for all in Israel/Palestine, including for Palestinian refugees."
The letter states that the collective "recognise the underlying power imbalance between Israel, the occupying power, and the Palestinians, the people under a system of military occupation and apartheid, as described by Human Rights Watch, B’Tselem, Israel’s leading human rights organisation, and by Palestinian and international human rights experts."
On January 3, Watson posted her message of solidarity by reposting a graphic from the Bad Activist Collective on Instagram. The image reads: "Solidarity is a verb," written over a photo of demonstrators taken at a Free Palestine rally.
The post is captioned with a quote from scholar Sara Ahmed: "Solidarity does not assume that our struggles are the same struggles, or that our pain is the same pain, or that our hope is for the same future.
"Solidarity involves commitment, and work, as well as the recognition that even if we do not have the same feelings, or the same lives, or the same bodies, we do live on common ground."
Watson's post was criticised by Gilad Erdan, Israel's ambassador to the United Nations, who tweeted: "Fiction may work in Harry Potter but it does not work in reality. If it did, the magic used in the wizarding world could eliminate the evils of Hamas (which oppresses women & seeks the annihilation of Israel) and the PA (which supports terror). I would be in favour of that!"
She was also accused of "being an anti-Semite" by Danny Danon, a former Israeli ambassador to the United Nations. Danon tweeted a screen grab of Watson's post, with the caption: "10 points from Gryffindor for being an anti-Semite."
In their letter, the Artists for Palestine UK say that they "condemn all forms of racism, including anti-Semitism and Islamophobia.
"Opposition to a political system or policy is distinct from bigotry, hatred and discrimination targeting any group of humans based on their identity," the letter reads. "We see the former as a legitimate and necessary form of political and ethical expression and the latter as racism – pure and simple."