The union leadership has argued that AT&T is best-positioned to expand a national broadband network and has a better record of working with organized labor. AT&T employs about 43,000 CWA workers.
George Kohl, the union's senior director, said AT&T respects workers' right to organize.
"Sprint would not," he said.
Kohl said Sprint has fought unions and contracted with an outside telecom gear maker, Ericsson, which outsources work to India.
Taylor, the Sprint spokesman, rejected the contention his company is anti-union.
"Our view is we support our employees' right to organize," he said. "So far our employees have rejected union representation."
Sprint has joined with public interest groups and other companies that oppose the sale to spearhead a grass-roots effort to gin up opposition to the deal. The No Takeover Project, unveiled at a press conference Tuesday, includes a website that directs people to contact lawmakers and the FCC as well as tweet officials.
In the battle to sway Congress and the federal agencies, AT&T is poised to vastly outspend Sprint. The company shelled out more than $6.8 million on lobbying in the first quarter of this year, compared with $583,000 by Sprint, according to filings with the Senate.
In the first three months of this year, AT&T's political action committee has contributed $694,000 to political candidates and parties. Sprint's PAC has made $39,000 in political contributions during the same period.
But Sprint has increased its Washington presence, tapping three lobbying shops in recent months to help make its case. The new hires include the Fritts Group and Franklin Square Group, which represents high-tech companies. Sprint has also contracted with Thorsen French Advocacy, whose principals are Alec French, former counsel to the House Judiciary Committee, and Carl Thorsen, once an aide to then-House Majority Leader Tom DeLay (R-Texas).
AT&T has also added to its lobbying roster, bringing on Peck, Madigan, Jones & Stewart, the Capitol City Group and Roberti Associates. According to his biography on the firm website, Vincent Roberti, a principal in the Roberti Group, "is credited as being instrumental in shepherding through the $67 billion merger of AT&T and BellSouth."
Both AT&T and Sprint have purchased ads in inside-the-Beltway publications to reach lawmakers.
The coming months will test whether consumer brand loyalty can translate into political strength and overcome the momentum of the merger. Even Beren, who edits the T-Mobile blog, said he is preparing for the possibility of the sale being approved.
"I have already purchased a number of AT&T domain names," he said.
Rep. Elijah Cummings, D-Md., right, hugs Harold Schaitberger, General President of the International Association of Fire Fighters, after the Congressman spoke at the IAFF's Legislative Conference General Session at the Hyatt Regency on Capitol Hill, March 9, 2015. The day featured addresses by members of Congress and Vice President Joe Biden.