U.S. officials are discussing launching a formal review into whether Tether and other stablecoins threaten financial stability, scrutiny that could lead to dramatically ramped-up oversight for a fast-growing corner of the crypto market.

After weeks of deliberations, the Treasury Department and other federal agencies are nearing a decision on whether to launch an examination by the Financial Stability Oversight Council, said three people familiar with the matter who asked not to be named in commenting on closed-door discussions. FSOC has the power to deem companies or activities a systemic threat to the financial system — a label that typically sets off tough rules and aggressive monitoring by regulators.

Such a designation would likely be a gamechanger for stablecoins, which are considered crucial to the crypto market because traders widely use them to buy Bitcoin and other virtual currencies.

Stablecoins have thrived in the unregulated shadows, with tokens in circulation now worth more than $120 billion, according to CoinMarketCap.com. And they are increasingly being used for transactions that resemble traditional financial products — like bank savings accounts — without offering anywhere near the same level of consumer protections.

A hallmark of stablecoins is that they are pegged to fiat currencies, meaning they are supposed to be immune to the wild price swings that have plagued Bitcoin. Tether and other firms achieve that by backing their tokens with assets like U.S. dollars and corporate debt.

The President's Working Group on Financial Markets, which is led by Treasury Secretary Janet Yellen, has been particularly focused on Tether's claims that it holds massive amounts of commercial paper — debt issued by companies to meet their short-term funding needs. In a private meeting U.S. officials held in July, they likened the situation to an unregulated money-market mutual fund that could be susceptible to chaotic investor runs if cryptocurrencies plunge.

Read More: Why Yellen, Powell Cast a Wary Eye on Stablecoins

The President's Working Group plans to issue stablecoin recommendations by December, and a consensus is building among regulators involved that an FSOC review is warranted, the people said. The groups overlap, as Yellen, federal reserve Chairman Jerome Powell and Securities and Exchange Commission Chair Gary Gensler are members of both the PWG and oversight council.

A Treasury spokesman declined to comment.

The FSOC process includes a lengthy study and an assessment of which federal agencies should respond and how. In the end, the council could direct those agencies to intervene in the market and reduce the dangers posed by stablecoin transactions.

While Tether is the most popular stablecoin, there are multiple rivals, including Coinbase Global Inc.'s USDC token and a dollar-linked offering from Binance Holdings Ltd.

Scrutiny has been ratcheting up as stablecoins proliferate. Coinbase made headlines this week by disclosing the SEC had threatened to sue if the crypto exchange launched a product that would allow customers to earn 4% yields for lending out their USDCs to other traders. The SEC believes the Coinbase proposal is an investment contract that should be registered with the agency, a view the company aggressively contested in a blog post and a series of tweets.

Watchdogs have also privately expressed worries about Diem, a stablecoin being developed by an association that includes Facebook Inc. A top concern is that the token's market impact could be massive because of its potential for widespread adoption — Facebook's social media network has almost 3 billion active users.

Treasury held meetings this week with industry representatives to ask them about the potential dangers associated with stablecoins. As it and other agencies consider taking action, they're facing intense pressure from Capitol Hill.

“I urge FSOC to act with urgency and use its statutory authority to address cryptocurrencies' risks,” Senator Elizabeth Warren wrote in a July 26 letter to Yellen that flagged the stablecoin market's interconnectedness and its susceptibility to investor runs. “The longer that the United States waits to adapt the proper regulatory regime for these assets, the more likely they will become so intertwined in our financial system that there could be potentially serious consequences.”

Stablecoins already face another threat from the U.S. government, as the Fed is discussing whether to launch its own digital currency. Powell told lawmakers in July that a central bank token would make stablecoins obsolete.

“That's one of the stronger arguments in its favor,” he said.