The group that organizes the presidential debates is rejecting complaints from the Trump campaign that the events are rigged this year because they are scheduled at times likely to draw a smaller audience.

Donald Trump, the Republican nominee, had expressed unhappiness that two of the three presidential debates overlap with National Football League games, meaning that night’s viewership would be divided between the two events.

“As usual, Hillary & the Dems are trying to rig the debates so 2 are up against major NFL games,” Trump tweeted Saturday, referring to Democratic opponent Hillary Clinton. “Unacceptable!”

The Commission on Presidential Debates, an independent organization that has sponsored the general election debates since 1988, said in a statement Sunday that it believes the dates, which it selected a year in advance, “will serve the American public well.”

The Commission, which doesn’t support, oppose or receive funding from political candidates or parties, is headed by former officials of the Democratic and Republican National Committees.

“It is impossible to avoid all sporting events, and there have been nights on which debates and games occurred in most election cycles,” the Commission said in its statement. “A debate has never been rescheduled as a result.”

The first presidential debate of 2016, scheduled for Sept. 26 at Hofstra University in Hempstead, N.Y., runs up against “Monday Night Football” on ESPN. The second, Oct. 9 at Washington University in St. Louis, clashes with “Sunday Night Football” on NBC.

The Commission announced the dates and sites of the debates in September 2015. The NFL announced its 2016 schedule in April this year though it has traditionally scheduled games on Sundays, Mondays and, more recently, Thursdays.

The final debate is set for October 19, a Wednesday, at the University of Nevada-Las Vegas. There is also a vice presidential debate scheduled for Oct. 4, a Tuesday, at Longwood University in Farmville, Va.

An expanded version of this report appears on WSJ.com.