The union, the powerful lobby of TV and film writers, has asked the Federal Communications Commission, which is investigating the deal, to hear views from the creative sector of the media industry.
The Guild said its objection to the deal is based on the grounds that "the continued separation of EchoStar and DirecTV is the only hope of having three competitors for television services to the typical home". The third competitor is cable.
The deal, announced in November, would see the creation of a satellite TV provider with almost 17m subscribers, which at the time was set to be larger than any of the cable companies.
Competition authorities have been investigating the merger because of concerns that it would limit the choice of TV supplier to households in rural areas.
EchoStar has been defending the move, saying that there are other competitors in the smaller satellite dish networks. However, an old anti-trust lawsuit against DirecTV, in which EchoStar chairman Charles Ergen claimed that the smaller dish networks were irrelevant, has come back to haunt him.
The deal is also opposed by a group of 80 members of Congress, who have formed a coalition to take their fight against the deal to Attorney General John Ashcroft and Federal Communications Commission chairman Michael Powell.
The proposed merger between EchoStar and DirecTV had been set to become the largest TV provider in the US. However, at the end of last year, AT&T agreed to merge its cable unit with Comcast creating a network with 22m homes.
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