HARTFORD, Conn. — Election reform activists are pressing Connecticut lawmakers to revive legislation vetoed by Governor Dannel P. Malloy that would strengthen disclosure requirements for groups that independently spend money or run ads for political candidates.

The advocates, including the good-government group Common Cause, have been hoping for a special session to draft new legislation before outside money begins flowing into the state for the November elections.

Closed-door talks have been held in recent weeks between Malloy’s office and Democrats in the House of Representatives and Senate over the issue of campaign finance reform. Discussions are expected to continue over the summer.

‘‘We don’t have the transparency laws we need to find out who is trying to buy our elections,’’ said Karen Hobert Flynn, vice president for the national Common Cause organization.

Flynn said since the US Supreme Court’s Citizen United ruling in 2010, special interests have injected large sums of money into state political races by using ‘‘shell organizations’’ to hide their identities. That money, she said, has been used to attack state-level candidates in Maine, North Carolina, and other states.

Supporters of the bill in Connecticut’s General Assembly do not have enough votes to override the governor’s veto to resurrect the original legislation during Monday’s scheduled veto session. There are also no plans to override any other of Malloy’s vetoes, a Senate Democratic spokesman confirmed on Friday.

Senator Gayle Slossberg, Democrat of Milford, cochairman of the General Assembly’s Government Administration and Elections Committee, acknowledged she doesn’t know if legislation can be passed during a special legislative session before this year’s election gears up. But she and her cochairman, Representative Russell Morin, Democrat of Wethersfield, said they are committed to keeping the issue alive.

‘‘We put together what we considered to be a very strong disclosure law that would pass constitutional muster,’’ Slossberg said. ‘‘We were disappointed obviously when the bill was vetoed. We’ll just continue to keep advocating for it.’’

But as the summer progresses, Morin said the chance that something will get passed before the fall election season becomes less likely.

‘‘I would like to, but I'm not overly confident that we’ll get there,’’ Morin said.

In his veto message, Malloy, a Democrat, predicted some portions of the bill would likely violate the US Constitution, while other sections ‘‘represent poor public policy choices.’’

Roy Occhiogrosso, Malloy’s senior adviser, confirmed that talks have been going on with state lawmakers, but said no agreement has been reached.