The major objections to same sex marriage come from the religious community most especially the religious right and ultra conservatives.
As for the general population in the United States a Gallup Poll dated May 20, 2011 revealed that a majority of Americans, 53%, now favor same sex marriage as a means to provide equal rights under the law. People are finding it more and more difficult to justify discrimination against gay citizens.
You can read more about it at the related link.
In the United States, there are too many to accurately count, but among them are the National Organization for Marriage, the Catholic Church, the Church of Jesus Christ of Latter Day Saints (aka the Mormons), the Republican Party and the Westboro Baptist Church.
Groups opposing same-sex marriage include the National Organization for Marriage ("NOM"), the Catholic Church, the Knights of Columbus, the Republican Party, the Tea Party Movement and the Church of Jesus Christ of Latter-Day Saints (a/k/a the Mormon Church).
Most Christian denominations, Catholics, Muslims, Orthodox Jews and Mormons oppose same sex marriage.
lobbyist
National Rifle Association
interest group
To eat banana pudding.
Protests
A lobbyist
Lobbyists are paid while interest groups aren't
lobbyist or political action committee
Special interest lobbyist influence congressmen by providing them information. Interest groups are specialist on the topic they are interested in and do a lot of research on that topic. Congressmen are generalist and rely on interest groups to give them information on important topics so they are more informed. Each interest group wants to inform the congressmen on their view of the data they have collected.
Today a lobbyist often writes a bill and then takes it to a congressperson that will sponsor it. They are also working and in/out congressional offices speaking with members.
Representatives.. I think. That or Senators.
Lobbyist