The alliance has spoken in defence of the humane society, which was criticised by a group calling itself the Center for Consumer Freedom (CFA).
Alliance representatives John Holland and Vicki Tobin said while some groups appeared content to run disinformation campaigns, the non-profit CFA appears intent on attacking the messengers.
"The most recent target of their attack is the HSUS," said Holland and Tobin.
"The HSUS, through their legislative arm, has been extremely successful in promoting animal welfare through legislation as well as litigation.
"The EWA considers the CCF attack as a blatant attempt to discredit HSUS, a mainstream organisation supported by an overwhelming number of Americans in backing the federal legislation to end the slaughter of American horses."
CCF recently circulated an email soliciting funds to create a $US75,000 documentary targeting the HSUS.
"This email was conveyed to EWA by dues-paying American Quarter Horse Association members who are opposed to horse slaughter," Holland and Tobin said.
The email read: " ... We are seeking one-time contributions to finance the production and distribution of our own short online documentary about the Humane Society of the United States. It will be similar to the news coverage HSUS has managed to bully off the Internet, but the group will not have any legal right to impact its distribution.
"We are trying to raise $75,000 during the next week to finance this project, and we need your help today! ..."
In past reports, major news outlets, including USA Today, and the Washington Post have gone on record condemning CCF for misleading the public. ABC News exposed CCF as a "front" group for lobbyists hiding behind a non-profit.
In a response, the HSUS says: "The Center for Consumer Freedom (CCF), while organised as a 501(c) (3) charity, is a flack agency and industry front group for tobacco, alcohol, and agribusiness interests."
Contrary to CCFs allegations, the HSUS has never portrayed itself as a "rescue" nor the umbrella organisation for local humane societies but as an organization that is involved in animal welfare on all fronts, from dogs, to cats, to gerbils and to horses.
Its emergency services team was recently instrumental in the rescue of Mustangs from a ranch in Nebraska and did indeed provide a home for eighty-four of the Mustangs as well as saving thousands of dogs from life in a puppy mill.
The EWA points out that a fight is brewing in Washington over equine issues, including slaughter (HR 503), Mustang protection (HR 1018) and humane transport (HR 305).
With President Obama taking a strong stand against lobbyists, EWA anticipates an increase in lobbying organizations masquerading as non-profit advocacy groups to hide their real agenda.