As federal prosecutors probe the business dealings of Senate Majority Leader Dean Skelos and his son, Nassau County Executive Edward Mangano and GOP lawmakers have introduced legislation that would force lobbyists working to persuade officials on bills and contracts to disclose their activities to the public.

The measure would require lobbyists to report to the county about the scope of their work, including the identities of their clients and the officials they lobbied, the lobbyists' compensation, a description of the issues they were paid to influence, and expenses incurred by the lobbyist in excess of $50.

"This new law will bring additional transparency by requiring contractors and vendors to disclose their lobbying activities," Mangano said.

Lobbyists are already required to register and report these same details to the state's Joint Commission on Public Ethics, but Nassau has never had its own mandated reporting system. The state requires disclosure only from registered lobbyists.

Nassau's bill would expand the definition of lobbying to include "any attempt to influence" officials and lawmakers on county issues, even if the individual is not registered to lobby with the state, officials said.

Nassau Democrats plan to introduce their own measure Tuesday, which would require attaching a lobbyist disclosure statement to all county contracts.

The dueling bills come less than a week after new reports disclosed that Dean Skelos (R-Rockville Center), and his son, Adam, were under investigation by Preet Bharara, the U.S. attorney for the Southern District of New York.

Bharara is reportedly probing a $12 million county contract awarded in 2013 to AbTech Industries, an Arizona-based environmental firm that employed Adam Skelos as a consultant.

Even though Adam Skelos is not registered with the state as a lobbyist, he would have been forced to report his activities under Nassau's new bill because of his consulting work with AbTech, said Mangano spokesman Brian Nevin.

Adam Skelos introduced introduced county public works employees to the company, a source has said. Legislators from both parties who approved the contract said they were unaware of Adam Skelos' connection to the firm.

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While AbTech submitted a higher cost estimate than one of the other two bidders, the county deemed AbTech the most-qualified firm based on "professional judgment."

The Nassau legislation would require lobbyists earning at least $1,000 in compensation and expenses to register annually with the county attorney's office at a cost of $200.

Lobbyists also would need to file a quarterly report detailing their work and file an annual report detailing their activities during the previous year. All of the reports would be available to the public on a county website.

Lobbyists who violate the law would face up to one year in jail and a fine of $5,000. Lobbyists who file their reports late could face a $500 fine.

Blair Horner, legislative director at the New York Public Interest Research Group, said the measure should make it easier for Nassau residents to know who is working behind the scenes to shape legislation, secure appointments and win contracts. "Nassau residents would have a keener sense if what is being spent to influence decision makers," he said.