"The letter is written to indicate that many senior members of the international scientific community show solidarity with politicians, artists, sports people and many others who have already expressed their abhorrence for the Russian Government's actions against its gay citizens," wrote McKellen and British chemist Harold Kroto, who won the 1996 Nobel Prize.
"I have been warned by the UK Foreign Office that in Russia I could not speak openly about my sexuality, at least in the hearing of anyone under the age of 18," McKellen said. "I have therefore felt that I had to turn down invitations to attend Russian film festivals."
"Protest is never easy but we hope that by expressing opposition to the new legislation it might be possible to encourage the Russian State to embrace the 21st Century humanitarian, political and inclusive democratic principles which Mikhail Gorbachev worked so hard to achieve," they added.
With characteristic aplomb, McKellen signed his name, " Ian McKellen (aka Henry V/Gandalf)."
Russia's anti-gay policies have become a diplomatic headache for the country, which will host the Winter Olympics in Sochi next month. President Barack Obama, and several European leaders, won't be attending the games -- Russia refused to call his absence a "boycott" -- but he will send three openly gay athletes with the U.S. delegation.
The International Olympic Committee has promised that gay athletes won't be subject to discrimination when they enter the country.