Just two months before lawmakers grilled executives from Amazon, Apple, Facebook, and Google at a hearing held as part of a broader antitrust probe, some of Amazon's top executives made donations to the chair of the subcommittee leading the investigation.

Over a three-week period starting in late May, five senior executives from Amazon made individual contributions to Rep. David Cicilline, the Democrat from Rhode Island who's leading the House antitrust investigation into major tech companies, public filings show. Cicilline became the chairman of the House Judiciary Committee's Antitrust, Commercial and Administrative Law Subcommittee in January, when Democrats regained control of the House.

The executives include Amazon's CEO of worldwide consumer Jeff Wilke, CFO Brian Olsavsky, general counsel David Zapolsky, SVP of worldwide operations Dave Clark, and SVP of North America consumer Doug Herrington. They all contributed the max $2,800 allowed, except for Olsavsky, who donated $1,500.

No executive from other companies under the House antitrust investigation — Apple, Facebook, and Google — made individual contributions to Cicilline's campaign this year, filings show.

The donations serve as an example of how companies and executives work behind the scenes with lawmakers to try to advance their corporate interests -- albeit with mixed effectiveness. Corporate officers have always made individual campaign donations, but experts say the timing of Amazon executives' payments likely reflects the company's heightened urgency over growing regulatory scrutiny.

"It suggests a greater sense of pressure or threat of regulation from Congress, especially given the growing bipartisan attention being directed to this issue," said Alexander Hertel-Fernandez, a political science professor at Columbia University.

Amazon's spokesperson declined to comment for this story. Cicilline's representative told CNBC in an email that, on the day the subcommittee launched its antitrust investigation, the chairman put in place "a formal policy of refusing campaign contributions from companies and executives that may be subject to scrutiny." The donations by Amazon executives were made before the antitrust probe announcement, and before the July hearing was scheduled.

Amazon executives have other reasons to support him. Cicilline introduced the Equality Act, which prohibits employee discrimination on the basis of sexual orientation or medical condition, and was a key supporter of raising the federal minimum wage -- two initiatives the company supports. Those are the only two issues that all of Amazon's registered lobbyists have lobbied for in the past, according to a person familiar with the matter.

At the same time, filings show that only one Amazon executive has donated to Cicilline in the past: Vice President of Public Policy Brian Huseman contributed $250 in 2012.