HARTFORD, Conn. (AP) — Gov. Dannel P. Malloy vetoed a bill on Friday that would have required corporations and other groups that independently spend money or run ads for political candidates in Connecticut to identify their top donors.

The bill was partly a response to the U.S. Supreme Court's Citizen United ruling in 2010, which changed restrictions on campaign spending.

In his veto message, Malloy predicted some portions of the bill would likely violate the federal constitution, while other sections "represent poor public policy choices."

"While I have advocated for transparency in the elections and campaign finance process for a long time, and could certainly support sensible reform in this area again, I cannot support the bill before me given its many legal and practical problems," he wrote, adding that some parts of the legislation would "have a chilling effect on issue advocacy and neutral debates about matters of public concern."

Cheri Quickmire, the executive director of Common Cause in Connecticut, a pro-reform organization, said Malloy has "squandered an opportunity to pass the strongest disclosure bill in the country" because it strengthened the state's existing public campaign financing system for state candidates. Malloy, a Democrat, was the first governor elected using the program.

"Unfortunately, the citizens of Connecticut will now be left in the dark about who is funding the millions of dollars that will be spent in Connecticut state races this fall, which leaves our state open to the corrupting influence of independent expenditures."

Karen Hobert Flynn, vice president for the national Common Cause organization, said since the Citizen United decision, special interests have injected large sums of money into state political races around the country by using "shell organizations" to hide their identities. That money has been used to attack state-level candidates in Maine, North Carolina and other states, she said.

But Malloy said the bill defined the term independent expenditure "so broadly it would encompass virtually any communication referring to a public official, who is also a candidate for office." He said it would include interviews with candidates and debates that use resources of media outlets.

Under the bill, the board of a corporation or other group to vote to authorize campaign-related disbursements of more than $4,000. The corporation or other organization must disclose on its website the votes of board members and details on the expenditure within 48 hours of the vote.