This followed the request of some clubs to have their players feature in midweek's league matches.
Okon said the affected players must head to camp immediately after the league games or face severe sanctions.
"The players know themselves and to that effect they are expected in camp on Thursday.
"With just seven weeks to the start of the championship l do not expect any player to drag the team backward," he said.
The Fifa Under-20 Women’s World Cup holds August 18 to September 8 in Japan.
Falconets resumed for training in the Abuja on Sunday after six- week break.
Only 19 players out of the invited 35 have reported to team's Serob Hotel, Abuja.
They are captain, Gloria Ofoegbu, Uchechi Sunday, Ugo Njoku, Chisom Henry, Lola Phillips, Vivian Okotie, Ebubeleye Whyte, Chinyere Okafor and Blessing Edoho.
Others include Chioma Nwankwo, Fausilat Adeyemo, Chidinma Okoro, Ugochi Okafor, Bukola Ogunnoiki, Juliana Osuji, Osarenoma Igbinovia, Grace Henry, Winifred and Tina Chinyere.
Nigeria are drawn in Group B against Brazil, Italy and Korea Republic.
Falconets will start their title chase against Korea on August 19 in Saitama.
The nation's representatives did not concede a goal during the Africa qualifying series that ended on May 19 with a 3-0 drubbing of Congo DR in Kinshasa.
