KKR and Bain Capital have agreed to pay $20m to workers who lost their jobs in the Toys R Us bankruptcy, in a high-profile victory for employee advocates who have blamed Wall Street firms for the retailer’s demise.

The unprecedented move follows a months-long campaign in which former employees pressured some of America’s largest state pension funds to cut off investment in firms connected to the doomed buyout of the retailer.

“We’ve not finished fighting and we’re not going away,” vowed Ann Marie Reinhart, who worked as an assistant store manager in North Carolina. She said she was just days from the end of her 29-year career at Toys R Us when she learnt she would not receive the severance pay she was expecting.

The hardship fund announced on Tuesday falls far short of the $75m workers have been seeking to cover payments they claim were promised and then snatched away when creditors opted to liquidate the company in March.

KKR and Bain said they had “never experienced something like this in the history of either firm” and “hope[d] others [would] consider joining and contributing”.

But so far, no further promises of help have been forthcoming, according to people familiar with the talks.

Vornado Realty Trust, which was an equal partner with Bain and KKR in the 2005 buyout, has refused to answer workers’ emails, the Financial Times reported earlier this year.

Two hedge funds that were key Toys R Us creditors have also refused to join the discussions, saying they were not to blame for the company’s ills. “We do not believe there is a sound basis to claim that Toys R Us secured lenders should make additional financial contributions for the benefit of employees,” a lawyer for the two funds, Angelo Gordon and Solus Alternative Asset Management, wrote earlier this year.

Their combative stance prompted workers to ask a state investment board in New Jersey, where Toys R Us was based, to reconsider their investments with a Solus fund. Anthony Scaramucci, the hedge fund manager and former White House communications director, has said he encouraged Solus to help workers.

It is highly unusual for private equity firms to commit extra cash to stricken companies where there is no prospect of recovery.

Bain and KKR stressed that none of the hardship money would come from their investors, suggesting that the partners had dipped into their own pockets to try to draw a line under their role in a contentious corporate failure.

Hardship payments would be available to Toys R Us workers of at least one year’s standing whose annual income was between $5,000 and $110,000 if they meet certain additional criteria, the firms said.

The money will be distributed by Kenneth Feinberg, a lawyer who specialises in compensation for victims of large-scale disasters. He has previously administered funds created after the Deepwater Horizon oil spill and the 9/11 terrorist attacks.