Kaepernick, 29, endured a lot of hateful commentary previous year when taking a knee during the playing of the national anthem before games.
NY has already been the site of gatherings supporting Kaepernick, as about 75 officers came together on Saturday.
The threat of a nationwide boycott is meant to send a message to NFL Commissioner Roger Goodell and the owners of the NFL's 32 teams, Riggs said.
According to the Associated Press, the 81-year-old Serpico said he's not a football fan but believes Kaepernick is being unfairly blacklisted from the NFL for his political protest.
"He's trying to hold up this government up to our founding fathers", Serpico said.
"I am not going to stand up to show pride in a flag for a country that oppresses black people and people of color", Kaepernick said last August.
Serpico uncovered widespread corruption in the NYPD while working undercover in the late 1960s and early 1970s.
When Al Pacino asked Serpico why he chose to take on the cause, he replied: 'I guess I would have to say it would be because.if I didn't, who would I be when I listened to a piece of music?'
The participants raised their fists and took a knee together near the end of the rally in a symbolistic display of support for Kaepernick.
Controversial quarterback Colin Kaepernick deserves a chance to continue his National Football League career, his supporters said Saturday.
The former football star came under heavy criticism for kneeling during the national anthem, and this season, he's struggled to get on a roster.
"The way he's being railroaded for speaking the obvious truth, this is not what America was founded on", NYPD Sergeant Edwin Raymond said at the rally.
"And that's the issue of racism in America and policing in America".
Kaepernick has not made a statement on his current free agency since he stepped away from the 49ers in March, but the rumors coming out of his camp are that he still wants to play quarterback in the NFL.
Kansas City Chiefs quarterback Alex Smith said he found it "crazy" that his former 49ers teammate did not have a contract for the 2017-2018 season.
'Young, strong, I felt like he had a long career ahead of him.