Opponents of AT&T’s proposed merger with T-Mobile filed last-minute petitions to federal regulators Tuesday in hopes of blocking the $39 billion mega-deal. But they are going up against a deep-pocketed telecom giant that’s just getting started on its own campaign to influence the decision.

Sprint Nextel, Leap Wireless, rural carriers and consumer advocacy groups told the Federal Communications Commission that the proposed merger would hurt the companies’ chances of survival and remove T-Mobile as a low-cost alternative to Verizon and AT&T, the nation’s biggest carriers.

AT&T argues that the merger would allow U.S. homes to get access to wireless high-speed Internet service sooner than without the deal. “Strong support for the AT&T-T-Mobile merger has been voiced by dozens of community, civic and minority organizations, 14 governors, multiple labor unions and elected officials,” AT&T spokesman Michael Balmoris said.

According to the Center for Responsive Politics, AT&T spent $6.8 million in the first three months of 2011 to hire lobbying shops and lawyers, who in large part are making the case to federal officials to approve the deal. AT&T’s lobbying expenditures are the third-largest among companies and trade groups so far this year, the center’s figures showed. The company is on track to spend more than the $15 million it paid lobbyists in 2010 to argue against policies such as Internet access rules and cellphone billing regulation.

Aside from money spent directly on lobbying government officials, industry observers say, AT&T is receiving support from several political leaders, trade groups and organizations such as the NAACP and at least one affiliate of the National Urban League. All have direct financial ties to the telecom giant.

Among the 14 governors listed by AT&T as supporters of the proposed merger is Bobby Jindal (R) of Louisiana. AT&T is a key sponsor of the Supriya Jindal Foundation, a charity of the governor’s wife.

The FCC has received about 300 letters of support for AT&T. Several stand out:

AT&T-sponsored Virginia Asian Chamber of Commerce urged the FCC to quickly approve the deal, saying that as a group “striving to create bridges between cultures, we look forward to the foundation that this merger will create and the opportunities that it will give the public.”

The Urban League of Portland sent a similar letter to the FCC, saying the merger could help minorities gain faster access to broadband through a more robust, combined company. AT&T donated $125,000 to $249,999 last year to the National Urban League’s annual convention, the group said on its Web site.

“When you are as big as AT&T, you try to make as many friends as you can get,” said Nick Nyhart, president of Public Campaign, a lobbying and political finance reform group. “Its strength is its size, and this is the approach by other big companies, not just in telecom.”

Nyhart and others say it’s hard to separate AT&T’s financial contributions to organizations that also advocate in favor of positions that benefit the company. Many groups that have come out in favor of the deal in recent weeks also receive support.

“They have curried favor with organizations who, whether through direct or indirect expectations, will go to bat for them,” said Ellen Miller, executive director of the Sunlight Foundation, a campaign finance reform group. “That’s what a sophisticated lobby does, and AT&T is among the top of this in Washington.”

AT&T’s political action committee gave $616,500 to lawmakers and political parties in the first three months of 2011, according to an analysis by the Sunlight Foundation. The phone giant has 31 lobbying firms registered with it; included among the lobbyists are former senators Trent Lott (R-Miss.) and John Breaux (D-La.).

Opponents of the deal are also ramping up their lobbying efforts. Sprint Nextel, the third-largest wireless provider, is hiring additional support, but its spending so far — $583,000 — is less than one-tenth of AT&T’s lobbying expenditures.