WASHINGTON — The partial government shutdown is slowing plans by some companies to issue stock to the public and potentially cutting off a key source of capital for the financial markets.

The shutdown, now in its fourth week, has all but darkened the Securities and Exchange Commission, the government agency that oversees the markets. Most of the SEC's 4,400-person staff is furloughed, including lawyers and other staffers who must approve corporate paperwork for initial public offerings. This process typically takes two to three months.

Companies that have been moving toward issuing initial public offerings of stock in the coming months include such high-profile names as the ride hailing firms Uber and Lyft and the image-sharing platform Pinterest. Among others are biotech and health sciences companies that depend on funding from public markets.