A gay rights campaign, in which a Jewish journalist is prominent, is to force each member of the House of Lords, including the Chief Rabbi, to record their position on gay marriage.
The "Out4marriage" campaign will ask every MP and peer to record a video, send a tweet or add their name to a list of those who back equal marriage. Those who do not respond or issue no comment will be added to a public list of those who do not support the move.
Lord Sacks has been under pressure to take a stand on government plans to introduce marriage for same-sex couples, being urged to "speak out" against the proposals by head of the Federation Beth Din Dayan Yisroel Lichtenstein.
The Chief Rabbi's Office has so far refused to comment on the issue. Both the Reform and Liberal movements have backed a plan to allow same-sex couples to have a civil marriage.
Ben Cohen, founder of gay news website Pink News, has been part of the team running the Out4Marriage campaign. This week, volunteers filmed supportive MPs, including Golders Green's Mike Freer.