Two Senate Democrats introduced a bill on Thursday that would take aim at activist hedge funds and their ability to act together in “wolf packs” to overtake public companies.

The bill would shorten the number of days that activists have to disclose newly acquired shares in a company and force the disclosure of derivatives and other holdings that now don’t have to be reported. It would also redefine the rules about who has to report when they have amassed a greater than 5 percent stake in a company.

The bill, by Senator Tammy Baldwin of Wisconsin and Senator Jeffrey A. Merkley of Oregon, comes after years of debate about reforming share ownership disclosures both at the Securities and Exchange Commission and among shareholder advocacy groups. Senator Elizabeth Warren, the Massachusetts Democrat, and Senator Bernie Sanders of Vermont, who is vying for the Democratic nomination for president, are co-sponsoring the bill.

Activism is on the rise. The pending merger of Dow Chemical and DuPont came after months of prodding by Nelson Peltz of Trian Fund Management. Carl C. Icahn threatened a proxy battle at the American International Group before the insurer agreed this year to give board seats to his firm and another activist, John Paulson of Paulson & Company.