Maryland's AFL-CIO, a 300,000-member strong labor union, will back the same-sex marriage legislation, marking a key endorsement from a powerful political force in the state.

The group last month passed a resolution supportive of gay unions, and will hold a news conference Thursday. The same-sex marriage debate is expected to be a fierce one this year, and advocates on both sides of the issue are already planning events.

The bill passed last year in the Senate, but was pulled from the House floor because Democratic leaders feared they were a couple votes short. House Speaker Michael E. Busch backs the bill and says there are between six and ten delegates who are on the fence about the legislation.

Strong labor support could help with those votes, and should the bill pass and be petitioned to referendum, labor is a strong ally in the field. Smaller unions have already joined a coalition supporting the bill.

Opponents too are planning events, including a prayer day this Sunday opposing gay marriage.