In recent years, some of the biggest names on Wall Street have made significant investments in railroads, reaping big stock gains as railroads reported higher profits. But the underlying strategies that strengthened railroads’ bottom lines have caused friction with customers, regulators and particularly workers — giving rise to a contract dispute that threatened a nationwide shutdown of the railway system.

After losing ground to trucking in the mid-20th century, the rail industry managed to recover through decades of consolidation and a push for efficiency. The New York Times reports that critics say those same dynamics created a system with thin staffing and minimal competition, making it particularly vulnerable to shocks like the COVID-19 pandemic.

The strategy is evident in head count, which has fallen at nearly all of the major railway companies in the United States and Canada. At CSX, for example, the number of employees plunged by a third over the past decade. This helped expand the company’s profit margins, and its stock is up over 300% since the end of 2011, far exceeding gains in the wider stock market.

Last year, the seven major railways based in the United States and Canada — which include CSX — had combined net income of $27 billion, up from $15 billion a decade earlier. Over the past decade, the six of those seven railways that were publicly traded paid out $146 billion in stock buybacks and dividends, which is over $30 billion more cash than they invested in their businesses.

For the employees who remain, pay has risen. At the four biggest U.S. railways, pay and benefits per employee rose by 26% over the past decade, slightly ahead of inflation, according to an analysis of the companies’ financial filings.

But employees say the reductions in staffing have resulted in more punishing schedules. Restrictive policies have kept them from seeking routine medical care, spending time with their families and otherwise living their lives, they say.