“TODAY'S decision will undoubtedly make some wonder whether the Supreme Court has now decided that some corporations are too big to be held accountable,” thundered Patrick Leahy, a Democratic senator, on June 20th. His ire was aroused by the court's decision to scotch a sex-discrimination lawsuit against Walmart, the world's biggest retailer. Like many on the left, Senator Leahy thinks that under Chief Justice John Roberts the court has an excessively pro-business bias.

This week's verdict affects 1.5m current or former employees who joined a class-action lawsuit against Walmart. (The lead plaintiff, Betty Dukes, is pictured above.) They claimed that Walmart systematically discriminates against women, citing statistical disparities in pay and promotions. Walmart retorted that it has rules against discrimination and enforces them vigorously. Since decisions about hiring and promotion are taken locally, by thousands of store managers, Walmart argued that it was unjust to cram so many separate events into a single lawsuit.

The court sided unanimously with Walmart on one question, concerning back pay. On the broader question of whether the 1.5m women constituted a single class, the court's five conservatives said no. They have “little in common but their sex and this lawsuit”, harrumphed Justice Antonin Scalia. The court's four liberals favoured sending the case back to a lower court to give the plaintiffs another chance to get their arguments straight.

The court's balance shifted in 2006, after George W. Bush picked John Roberts and Sam Alito (two conservatives) to replace William Rehnquist (a conservative) and Sandra Day O'Connor (a centrist). Since then, the kind of cases that the US Chamber of Commerce supports have been more likely to succeed. During 1994-2005, some 56% of the cases supported by the chamber and considered by the court succeeded; the success rate during 2006-10 was 68%. In 2009-10 the side supported by the chamber won in 13 of 16 cases, five of those by the slimmest of majorities (5-4).

A study by Lee Epstein, William Landes and Richard Posner, entitled “Is the Roberts Court Pro-Business?”, drew similar conclusions. It found that the Supreme Court ruled in a pro-business fashion in 29% of cases under Chief Justice Earl Warren (who served from 1953 to 1969). Under Warren Burger (1969-86) the figure was 47%. Between 1986 and 2005, under Chief Justice Rehnquist, it was 51%. Under Chief Justice Roberts it has risen to 61%.

Some cases particularly irk the left (see table). In 2007 the court threw out a sex-discrimination case filed by Lilly Ledbetter, an employee of Goodyear, a tyre company, because more than 180 days had passed since the company allegedly favoured her male co-workers in pay decisions. Her supporters argued that each new pay cheque should count as a fresh act of discrimination. By a 5-4 majority, the court disagreed.

In another case, the court refused to allow mobile-phone customers to sue AT&T as a class, instead limiting them to using the firm's arbitration process. The place “is making it more and more difficult for Americans to have their day in court,” fumes Mr Leahy, a former lawyer.

But is the court really guilty as charged? Clearly, it is less hostile to enterprise than the Warren court was. Still, it does not always let businesses win. On June 6th it unanimously threw out a lower court's decision that restricted the ability of investors to bring a “fraud on the market” lawsuit against Halliburton, an oil-services firm. In 2009 the court allowed a lawsuit to proceed against Wyeth, a drug firm, for not putting a clear enough warning label on a drug, though its label had been approved by the Food and Drug Administration.

Both decisions exposed businesses to more lawsuits. In the Wyeth case, the court's liberals were joined by Clarence Thomas, the most conservative justice, because he thought that state laws should trump federal regulations. “This stuff is far more complicated than the left's basic caricature,” says James Copland of the Manhattan Institute, a conservative think-tank.

It is not so much that the court is pro-business; it is more that a majority of justices think there are too many lawsuits, argues Tom Goldstein of SCOTUSblog, a forum for learned discussion of the court. The upshot, since businesses are generally the targets of lawsuits, is that “they tend to do pretty well,” he says.

Also, the federal government demands far more of business than it used to, which generates more disputes. “As late as 1965, there was no employment-discrimination litigation, no class actions for damages suits, no environmental law and no campaign-finance limitations,” observes Richard Epstein, a legal scholar at the conservative Hoover Institution. Small wonder the court's caseload has changed.

This week's decision will make it harder to assemble class-action lawsuits. Companies are delighted, as are those who think America's lawsuit culture does more harm than good. Trial lawyers are aghast, as are Democratic senators and those who distrust big business more than they distrust lawyers. However, the fury of this week's debate will seem like a blip compared with the battle brewing over Barack Obama's health reforms, which will surely come before the court before long.