Shares of Block (SQ  ), the payments platform formerly known as Square, tumbled on Thursday after Hindenburg Research entered a short position on the company, alleging that it facilitates fraud.

After a two-year investigation into the company's practices, Hindenburg charges in a report published Thursday that Block "has systematically taken advantage of the demographics it claims to be helping."

Those demographics include small- and medium-size businesses and individuals with limited access to banking services. The company's payment services include Square, which accepts credit card payments and popular amongst business owners, and Cash App, which allows users to easily transfer money between accounts.

The research firm consulted with former employees and partners as part of its investigation, as well as regulatory and litigation records for state and federal governments.

Hindenburg alleges that most of Block's success can be attributed to its "willingness to facilitate fraud against consumers and the government, avoid regulation, dress up predatory loans and fees as revolutionary technology, and mislead investors with inflated metrics."

Shares of Block fell about 15% on Thursday following the report, with the stock underperforming the broader market at a loss of over 4% year-to-date.

Notably, Hindenburg researchers highlighted on Cash App's practices during the pandemic, alleging that Block "ignored both internal and external warnings" that multiple users were using the same account number to receive government stimulus funds. One previous customer service employee estimated that 60% to 70% of the accounts they reviewed during a typical workday were linked to multiple other accounts, the report said. Another alleged that 40% to 75% of accounts were "fake, involved in fraud, or were additional accounts tied to a single individual."

Hindenburg also claims that CEO Jack Dorsey sought to boost Cash Apps' use during this period of financial distress by tweeting that "users could get government [stimulus] payments through Cash App 'immediately' with 'no bank account needed' due to its frictionless technology," the report said.

That increased use led to many states to try and reclaim some suspected fraudulent payments, the report claims. "Washington State wanted more than $200 million back from payment processors, while Arizona sought to recover $500 million," the report said, citing multiple former employees.

Other claims from employee interviews alleged that "pressure from management has resulted in a pattern of disregard for Anti-Money Laundering (AML) and Know Your Customer (KYC) laws."

Hindenburg Research has targeted about 30 companies since 2020, with their shares losing about 15% on average the day after the firm publishes a report, according to Bloomberg News. Shares also tended to be down over 25% on average after six months.