On Wednesday the authorities showed up unannounced to collect evidence and investigate supposed illegal activities.
According to officials the problem centred on the publication of the office's newsletter, which had not been given the necessary government approval.
"I suspect our anti-discrimination activities have offended many people, including big corporations, government officials, and wealthy businessmen," Lu Jun, a lawyer with Yirenping, told Al Jazeera.
Human Rights in China, a US-based rights group, said on Thursday that the raid on Yirenping showed the "increasingly restrictive legal environment under which China's civil society organisations must operate".
The raid on Yirenping is just the latest blow to the handful of organisations in China that push for social change and justice.
Last week police raided the offices of another Beijing law firm, Gongmeng, which offers legal aid specialising in human rights issues.
The raid saw police confiscate most of the firm's computers and office equipment.
In the months previously, several of Gongmeng's lawyers have had their licences revoked because of their work.
Teng Biao, one of the firm's lawyers, says the crackdown appears to be a warning to other organisations to rein-in their activities.
"It also sends a clear signal to other organisations fighting for human rights and the public interest to be more careful. It's very worrying"
"The fines slapped on our legal aid office, and the possibility of our closure, would be a blow to civil society," he told Al Jazeera.
"It also sends a clear signal to other organisations fighting for human rights and the public interest to be more careful. It's very worrying."
The groups targeted in the crackdown are China's social conscience.
They are the organisations which have helped families with babies sickened by toxic milk formula, or who have raised the profile of powerless groups, such as migrant workers and peasants.
Teng says the crackdown has had a devastating effect.
"Most human rights lawyers are based in Beijing. And over the last few months, I'd say the effect has been huge," he says.
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"I'm guessing about 70 per cent of rights attorneys have been harassed."
In most cases the authorities are using technicalities to handicap organisations.
Gongmeng, for example, has been targeted with a tax investigation.
But with the 60th anniversary of the founding of communist China approaching – a sensitive date in the country's political calendar - what many suspect is that this is a concerted effort to silence organisations that highlight difficult issues.
The assault on these institutions means that after the dust settles, if the government succeeds, there may well be no one left to fight for the public interest.