New York Assembly Speaker Carl Heastie accepted $13,800 in basketball hospitality from a company lobbying legislators for tax relief, less than three months before it secured a concession potentially worth more than $18m. No link between the hospitality and the tax decision has been proved.

The episode forms part of wider scrutiny of more than $1m in political donations spent on sporting events since Heastie became speaker in 2015. His office says the events raised more than $10m for Democrats; a former fundraising employee disputes whether some gatherings served that purpose.

In March, Heastie and at least four staff members attended a Boston Celtics home game in a VIP suite at TD Garden. Delaware North, the hospitality and gambling company that owns the arena, supplied the package. Three Celtics hospitality packages donated by the company were worth almost $37,000 altogether.

Company representatives met Heastie about gambling taxation in the weeks after the March game. The state budget approved in late May allowed gambling operators to retain more of their slot-machine revenue. An investigation estimates Delaware North could save more than $18m by 2029. Other companies also benefited.

Delaware North says it complied with the law, donated the suites for fundraising and held no political discussions with Heastie or his staff during the games.

The Assembly Democrats’ fundraising committee paid more than $588,000 to the New York Yankees and over $117,000 to a company arranging meetings with former players. Spending also covered other sporting events and, in some cases, food, drink and hotels.

Annual sports spending rose from an average below $5,000 before Heastie’s speakership to almost $90,000 afterwards. The equivalent Democratic committee in the state Senate raised similar sums over the past decade but spent less than a tenth as much on sport. More than $154,000 of sports expenditure was recorded as office expenses rather than fundraising costs.

The former employee said gatherings largely involved socialising and drinking, with politicians, staff, friends and partners attending alongside donors. He said Heastie’s then-partner, a lobbyist, attended one event.

Former state lobbying regulator David Grandeau described the arrangements as appearing corrupt, ranging from routine political practice to possible bribery. Columbia University law professor Richard Briffault said spending primarily for personal enjoyment could constitute unlawful use of donations.

New York restricts gifts from interested businesses, but donations to political committees fall under different rules. Personal use of political funds remains prohibited.

Heastie rejects suggestions of illegality or unethical conduct. His spokesman cited fundraising proceeds and recent Democratic election successes. The unresolved issue is whether the expenditure principally supported fundraising or private recreation.