The union claims the two companies underestimated the market share the combined company would have if their $8.2 billion merger is cleared by the Federal Trade Commission.
The heads of AT&T and DirecTV Groupon Tuesday twice defended their planned $67 billion merger from critics.
House and Senate hearings will be held Tuesday to examine AT&T's $67 billion plan to acquire DirectTV Group.
Move appears to be a request for an extension to wrap up CFIUS approval terms.
Expected divestitures convinced second suitor, widely believed to be Kroger, not to best Albertson's $9 billion offer.
House panel hears worries of programmers, small cable operators and Internet backbone providers.
Advocacy groups wanted a full investigation of privacy concerns raised by the companies' $19 billion merger.
The Democratic majority sitting on the Federal Communications Commission on Monday brushed aside a furious campaign by broadcasters and voted to restrict local television partnerships that critics say have been used to circumvent federal limits on local TV station ownership.
Whether food distribution is a national market will be key to the agency's view of the merger.
TV partnerships would be dropped in duopoly markets to appease regulators.