John Wells, the president of the Writers Guild of America, West, didn’t outright say that he was opposed to the Comcast-NBC Universal pact, but he sure had serious reservations.

The exec producer behind “ER” and “The West Wing,” as well as the current series “Southland,” is the highest profile creative type to appear before Congress to testify on the transaction.

“The combined entity being discussed today will control 20% of television viewing hours,” he told the Senate Commerce Committee. “Control of both content and distribution provide ample opportunity for abuses of power in the pursuit of corporate self-interest. In this case, we are concerned that bigger won’t be better.”

Wells acknowledged that he benefited after NBC canceled “Southland” last year and it found a home on TNT, but he said that the “proposed increase in vertical integration” will “threaten to undermine progress made in this area and lead to increased cost for consumers.”

He also expressed concerns that the merger would concentrate “a significant amount of local, national and online news programming within one company.”

The greatest danger of the merger, he said, was in its possible effect on the burgeoning online video market. He cited concerns that the combined entity would favor video content it owns or ventures in which it has a significant investment, shutting out independent producers.

He also pointed to Hulu, the vid service of which NBC Universal has a 30% interest, and said that it would “likely put it behind an authentication wall.”

“Consumers will no longer be able to watch TV episodes online without a cable subscriptions, which will reduce viewing of this content and, potentially, residual payments for writers and other talent.”

Comcast CEO Brian Roberts, however, noted that they will not have a controlling interest in Hulu, and said that he had not “personally met” with the Hulu team.

Moreover, he noted that Comcast will have a small share of what is a highly competitive landscape for online video.