Reed's support of civil unions has been criticized by some as not going far enough. Reed said in an interview Wednesday that he believes same-sex couples should have the same "full legal equality" as heterosexual couples.
Borders said couples in civil unions cannot get medical updates if their partner is hospitalized.
"As an African-American woman, how can I be against [marriage] equality?" Borders asked Wednesday, referring to the civil rights struggles of black Americans.
Reed said his position on civil unions is the same as in three states — New Hampshire, New Jersey and Vermont — where same-sex couples have the same rights and responsibilities as in marriage. Georgia has a constitutional ban against same-sex marriage.
Reed asked activists disappointed with his response at last week's forum to consider his record in the Legislature, such as co-sponsoring hate crimes legislation.
"I've cast votes where there were real-world consequences," he said.
Another frontline candidate, Councilwoman Mary Norwood, has received pressure from some bloggers who say she has refused to answer questions on lesbian and gay issues. Norwood released a statement late Tuesday saying she supports same-sex marriages.
"Anything less is out of keeping with Atlanta's history of openness and our celebration of diversity," she wrote.
Same-sex marriage has become a politically hot topic in recent years, with a handful of states permitting the practice. But last fall California voters approved a ban, and this week the state's Supreme Court upheld it, though it said the estimated 18,000 same-sex weddings that took place before the prohibition passed are still valid.
Lesbian and gay leaders say the mayoral candidates' stance on the topic sheds light on how sensitive they'll be to them and their issues if elected.
"It is important to know where [the candidates] stand because the mayor has a bully pulpit," Bailey said.