The top executives of more than 100 companies — including Starbucks, Microsoft and Mastercard — and trade groups are calling on Congress to backstop small businesses facing economic calamity.

In a letter dated Monday and addressed to congressional leaders of both parties, the executives painted a dire picture: mass business closures as coronavirus cases surge and the recession deepens.

The effort spearheaded by former Starbucks chairman and CEO Howard Schultz calls for federally guaranteed loans to last into 2021; flexibility in how that money is put to use; and at least partial loan forgiveness for the hardest-hit companies. It also said “funds must flow to all small business in need, particularly those run by people of color,” who have historically had less access to capital.

More than 4 million businesses have received emergency loans from the Small Business Administration after Congress approved $700 billion to support them in May. The letter said the nation’s 30 million small businesses need a more robust and sustained intervention from the federal government.

“We cannot stress enough the urgent need to act,” the letter states. “Every day that passes without a comprehensive recovery program makes recovery more difficult.”

Small businesses have been ravaged by the coronavirus pandemic, which forced businesses across the country to temporarily shut down and kept consumers largely confined to their homes. Unlike large, well-capitalized companies that can withstand economic shocks by drawing on their cash reserves, many small businesses have little by way of a safety net. They generate small profits, meaning their financial position is precarious even when the economy is strong.

And a large swath of those companies are never coming back: 55 percent of the 132,500 consumer-facing businesses that have shuttered since the pandemic began are now permanently closed, according to a report last month from the online review site Yelp. By Labor Day, the business leaders project another wave of permanent business closures if the government does not provide a financial life raft.

The call for long-term government assistance also highlights the potential cascading effects from the loss of small businesses which, the letter says, employ nearly half of all private-sector workers and account for 44 percent of the nation’s economic output. Smaller companies that depend on one another for parts, labor and technology face greater strain if neighboring business owners go under. And while larger companies can survive operating at limited capacity by borrowing money at rates that are close to zero, thanks to emergency measures from the Federal Reserve, smaller businesses have a far smaller financial cushion.

“By year end, the domino effect of lost jobs—as well as the lost services and lost products that small businesses provide — could be catastrophic,” the signatories said.

The small business crisis has been heightened by the expiration of expanded government aid for Americans who lost their jobs during the pandemic. Last week, nearly 30 million workers lost $600 in enhanced weekly unemployment benefits.

The business leaders also appealed to the broader role that entrepreneurship holds in American culture and the idea of the United States as a haven for small businesses. Nearly half of private-sector workers are employed by small businesses, the signatories noted. But that figure has fallen steadily in the last several decades, as big corporations command a greater share of the labor market and the economy—a trend that the coronavirus may accelerate.

Satya Nadella of Microsoft, Kevin Johnson of Starbucks, Ajay Banga of Mastercard, Ginni Rometty of IBM and Timothy Boyle of Columbia Sportswear were among the signatories, as were the top executives of U.S. Chamber of Commerce, Business Roundtable, National Restaurant Association and International Foodservice Distributors Association.