Cha-ching! Shannon Liss-Riordan has loaned Senate campaign $3 million since May

Shannon Liss-Riordan, a Brookline labor attorney, is running in the closely watched Senate primary.Jim Davis/Globe Staff

Shannon Liss-Riordan, a Brookline labor attorney running in the closely watched Senate primary, gave her campaign another $2 million last month, pumping up her war chest against Senator Edward J. Markey and Representative Joseph P. Kennedy III.

The sum pushes to $3 million the amount she has loaned her campaign since launching it in May. Combined with $220,000 she’s raised from donors, Liss-Riordan ended September with more than $2.8 million on hand, according to preliminary fund-raising records provided by her campaign Thursday.

Liss-Riordan has framed herself as a political outsider who’s long fought for workers’ rights, and she is leaning on her personal wealth to keep pace with Markey and Kennedy, both well-known and well-financed Democrats who together have commanded the attention and polling in the race.

The 50-year-old Democrat, who previously loaned her campaign $500,000 in May and June, said Thursday that she has not ruled out giving her operation even more money ahead of next year’s primary.

“I am up against two opponents who have been in Washington for a long time,” Liss-Riordan said, referring to Markey, who began his career in Congress in 1976, and Kennedy, a four-term congressman whose family name is synonymous with Massachusetts politics.

“I frankly don’t have access, nor do I want access, to the type of special-interest money that they’re going to be able to bring in,” she said. “I’ve known from the beginning that this was going to be a big fight, and that it was going to be costly.”

The seven-figure loan came from personal funds, according to Liss-Riordan’s campaign. She reported making $2.3 million through her law firm, Lichten & Liss-Riordan, over a 16-month stretch ending in May, according to her Senate financial disclosure.

Liss-Riordan had said she planned to devote more of her own money to her campaign after announcing an initial $1 million in loans in July. She deposited the additional $2 million on Sept. 20 — two days after the Globe reported that Kennedy, 39, intended to launch his own campaign.

Aides to Markey, Kennedy, and Democratic businessman Steve Pemberton said Thursday that they did not yet have fund-raising figures to release from the last three months. Candidates aren’t required to file reports with the Federal Election Commission until Tuesday.

Markey and Kennedy each had more than $4 million in their accounts at the end of June, according to their most recent disclosures. Pemberton announced his campaign in July.

How, and from whom, the campaigns raise their funds has been an early focal point in the primary. Markey and Kennedy have each said they are not taking corporate PAC money — and then traded barbs around their respective pledges. Kennedy also called on his fellow candidates to limit outside groups from pouring money into the race by agreeing to a so-called People’s Pledge. Liss-Riordan and Pemberton accepted; Markey, who made a similar pledge in his 2013 Senate race, has said he is considering it.

Liss-Riordan on Thursday also launched a new online ad campaign, backed by an initial $30,000, highlighting her legal record, which includes representing workers against Amazon, Uber, and Starbucks.

The 60-second spot features actors playing a coffee barista, a ride-hail driver, and a stripper. It plays off Liss-Riordan’s nickname of “Sledgehammer Shannon.” She has largely represented waiters, cleaners, and other low-paid workers who allege wage theft and misclassification as independent contractors by their employers.

In March, for example, Uber Technologies Inc. agreed to pay $20 million to settle California lawsuits, in which Liss-Riordan represented drivers, challenging the company’s classification of them as independent contractors.