When Americans lose track of money — in neglected bank accounts, paychecks they forgot to cash and elsewhere — state governments are increasingly aggressive in taking control of the cash.

Now, with those efforts swelling state coffers by more than $40 billion and lawmakers using some of it to patch budget holes, skirmishes are breaking out between states and companies with their own interest in holding on to the unclaimed property.

Companies accuse states of overreaching. State officials counter the businesses are more concerned with keeping the assets themselves. But critics say rightful owners too often get short shrift.

“The analogy is to finding somebody’s lost wallet. In Minnesota, anyway, we give people their wallets back. It’s just what we do here. But it’s not what the state is doing,” said Joe Atkins, a state representative from outside St. Paul who last year introduced a bill calling for increased funding to track down property owners.

While other states, too, have increased efforts to reunite owners with their property, many have changed laws to let them take control of more unclaimed property more quickly.

State lost-and-found programs have been growing rapidly for more than a decade. California alone has 28.5 million on its unclaimed property list.

States stepped up pursuit of unclaimed property in the late 1990s, after restructuring by insurance companies exposed those firms’ inability to locate many policy holders. Many states have hired auditing firms to scrutinize the books of insurers, retailers and others, paying them multimillion-dollar fees for unclaimed property they brought in.

The experience of two medical researchers who recently sued Delaware officials highlights the stakes.

Gilles Gosselin and Jean Louis Imbach, French chemists who developed a drug for treating hepatitis B, became shareholders of a company incorporated in Delaware to develop it. In 2009, without contacting them, Delaware took control of their stock, deemed abandoned, and sold it for $1.7 million.

As Gosselin and Imbach worked to track down their shares, the company was acquired by Merck & Co., in a 2014 deal that valued the researchers’ stock at $13.7 million. Delaware turned over proceeds of the earlier stock sale, but they took a $12 million hit.

“All of this could’ve been easily avoided if someone just sent a letter,” said Ethan Millar, a Los Angeles lawyer representing the researchers.

Most consumers on unclaimed property lists don’t even realize they’re entitled to missing money. It could be an inheritance they weren’t aware of or mutual funds entrusted to a broker with a mistaken address. Most are owed less than $100.

In all, state governments have $41.7 billion in unclaimed property on their books, according to the National Association of Unclaimed Property Administrators. Changes in law have accelerated collections.

Last year, Pennsylvania lawmakers shortened from five years to three the period before bank accounts and other property can be considered abandoned.

Money claimed by the state jumped to $669 million from $265 million the year before. Until the change, Pennsylvania returned about 43 percent of what it collected; afterward, payouts rose only slightly.