The drugs giant Merck has suspended its funding for the Boy Scouts of America, citing its discrimination against gay people.

The maker of top-selling drugs including asthma treatment Singulair and the HPV vaccine Gardasil joins Intel and UPS, which both pulled their funding following a campaign by lobby group Scouts for Equality.

In July, after a two-year consultation, the BSA reaffirmed its long-time policy barring openly gay members from joining the organisation and barring gay and lesbian people from serving as scout leaders. The ban sparked a national backlash and was condemned by both president Barack Obama and his Republican presidential challenger Mitt Romney.

Scouts for Equality, led by activist Zach Wahls, has petitioned all of the organisation's major sponsors in an attempt to get the BSA to overturn the ruling. Wahls is currently lobbying telecoms firm Verizon to pull its support for the BSA via petition website Change.org. So far over 63,000 people have signed the petition.

"I am thrilled that Merck & Company, a Fortune 100 pharmaceutical giant, has announced its foundation arm is immediately withdrawing funding from the Boy Scouts of America until the program ends its anti-gay membership policy," he said.

In a statement, Merck said: "Merck Foundation has suspended all funding to the Boys Scouts of America. The Merck Foundation will consider funding the BSA again when the organization's inclusion criteria has been expanded.

"The BSA's policy of exclusion based on sexual orientation directly conflicts with the Merck Foundation's giving guidelines. The foundation re-evaluated funding for the BSA when the organization restated its policy that excludes members on the basis of sexual orientation. Merck Foundation has notified the BSA of this decision."

The Merck Foundation has given $38,000 over the past three years to the Boy Scouts of America. Merck has also removed the BSA from its employee matching scheme. It did not say how much it had given to the BSA in this way.

There are over 2.7 million children and young adults in the BSA, and over 1 million adult members. The BSA formed a committee in 2010 to evaluate "whether the policy was in the best interests of the organization," and said it came to its decision after a two-year process of "extensive research and evaluations."

The BSA's policy states: "While the BSA does not proactively inquire about the sexual orientation of employees, volunteers, or members, we do not grant membership to individuals who are open or avowed homosexuals or who engage in behavior that would become a distraction to the mission of the BSA.

"Scouting believes same-sex attraction should be introduced and discussed outside of its program with parents, caregivers, or spiritual advisers, at the appropriate time and in the right setting. The vast majority of parents we serve value this right and do not sign their children up for Scouting for it to introduce or discuss, in any way, these topics.

"The BSA is a voluntary, private organization that sets policies that are best for the organization. The BSA welcomes all who share its beliefs but does not criticize or condemn those who wish to follow a different path."