In more than 30 states, if a corporate chieftain were to ask top executives to contribute to a politician, an inquisitive voter could easily learn that the firm was bankrolling the candidate.

But not in Maryland. Campaigns are not required to disclose the occupation and employer of large contributors.

That will change as of June 1 if Gov. Martin O'Malley signs legislation approved by the General Assembly that would require campaigns to gather such information from donors who give $500 or more to a single candidate during a four-year election cycle.

According to the governor's office, the bill is one of hundreds under review for a decision on whether to sign or veto. So far, O'Malley has used his veto power sparingly, and the bill's sponsors are confident he will sign it.

Passage of the measure was hailed by Common Cause Maryland and other campaign finance disclosure advocates as a significant step forward at a time when candidates for state office — like those nationally — are becoming increasingly dependent on donors with deep pockets to pay for mounting expenses.

"It creates more transparency within the campaign finance system," said Common Cause executive director Susan Wichmann. "It gives voters more information about what industries are funding campaigns."

The requirement that campaigns disclose a contributor's employer and occupation has been a fixture of federal law since the early 1970s, but Maryland had bucked the trend. "Maryland's playing catch-up – definitely," said Wichmann.

When the legislature finally adopted the measure in March, it did so by decisive margins. The final vote on the bipartisan Senate version of the bill, sponsored by Baltimore Democratic Sen. Bill Ferguson, was 46-0. In the House, the vote was 89-45, with most Republicans opposed.

Passage of the bill was one of several victories racked up this year by government reform advocates.

Among the others was a bill requiring that the ethics disclosure forms filed by legislators and other high-ranking officials be made available online. Another measure, also backed by Common Cause, will put a constitutional amendment on the November ballot that would force elected officials who commit crimes to leave office immediately upon a finding of guilt rather than lingering on the job until sentencing.

Legislators also created a task force that will examine other potential changes to the state's ethics laws — a possible springboard to further reform measures next year.

"I actually think we had a very successful session," Wichmann said.

The employer-occupation disclosure bill flows from a commission the Assembly created last year to study the state's campaign finance system. The panel, chaired by prominent lawyer Bruce Marcus, recommended that the legislature hold hearings on the idea of adopting a version of the federal requirement.

Del. Jon S. Cardin, the Baltimore County Democrat who was lead sponsor of the House bill, said voters have a right to know if, say, 20 individuals connected with a firm donate large sums to a candidate.

"That's probably useful information," said Cardin, who served on the commission.

He said voters might also want to know whether a candidate is receiving significant support from certain industries or professions, whether it be health insurers or trial lawyers.

According to Wichmann, researchers on campaign financing have been able to compile reports about industries supporting certain campaigns on the federal level and in other states, but have not been able to do so in Maryland.

If, for instance, researchers wanted to know whether a large law firm were heavily backing one candidate, under current law they would need to ferret out the names of all its lawyers and match them up with the campaign data base. Under the new law, they could extract that information with only a few mouse-clicks.

"It would help with a sort of a better aggregation by industry," said Ferguson.