By Chris Prentice and Michelle Price

WASHINGTON, July 1 (Reuters) - Robinhood Markets Inc, the online brokerage at the center of this year's retail trading frenzy, disclosed on Thursday previously unreported regulatory risks in its long-awaited initial public offering filing.

Amid an increasingly hostile climate in Democrat-led Washington, Robinhood's growing regulatory attention could be a turn off for some potential investors.

Aside from fines, Robinhood noted that government probes could result in business restrictions, increased compliance controls, changes to products and services and brand damage.

The company, which boasts 18 million customers, had drawn regulatory penalties for system outages and misleading disclosures even before it sparked outcry by curbing trading in some shares at the height of January's "meme stock" saga.

That episode sparked multiple probes and intensified scrutiny of Robinhood's business model.

To date, the startup has paid more than $136 million to settle regulators' allegations of wrongdoing, including a $70 million penalty announced by the Financial Industry Regulatory Authority (FINRA) on Wednesday.

While those penalties are small by Wall Street standards, Robinhood's legal expenses are growing fast, jumping from $1.4 million in 2019 to $105 million last year, the filings show.

Here are some of the regulatory threats that Robinhood noted in connection to its IPO.

'MEME STOCK' PROBES

Robinhood said that regulators had issued subpoenas or sought testimony and information from the company and CEO Vladimir Tenev as part of investigations into trading restrictions the brokerage imposed during January's meme-stock volatility.

The regulators included the U.S. Attorney's Office for the Northern District of California, the Securities and Exchange Commission (SEC), FINRA, the New York Attorney General's Office, other state attorneys general, Congress and some state securities regulators.

Perhaps the biggest revelation, though, was that authorities also took the unusual step of seizing Tenev's cell phone, Robinhood said, without elaborating.

OTHER INVESTIGATIONS, LEGAL RISKS

Robinhood also revealed what appeared to be a previously unreported probe by New York's Department of Financial Services (DYFS) focused on anti-money laundering and cybersecurity issues that the company expects to settle for around $15 million.

Additionally, in April, the California Attorney General's Office issued a subpoena seeking documents and information about Robinhood's trading platform, business and operations, and the application of California's commodities regulations to the platform. The company said it is co-operating with the probe.