The England and Wales Cricket Board has written to every team in The Hundred to remind them of their responsibilities around discrimination ahead of March's player auction.
The BBC reported earlier this week that the four Indian-owned franchises in the competition - Manchester Super Giants, MI London, Southern Brave and Sunrisers Leeds - would not consider signing Pakistan players due to ongoing tensions between the countries.
The ECB said in a statement earlier this week that they expected all eight side to "reflect" that the Hundred was open to players from anywhere.
Now it is understood that an email has warned action would be taken if there was evidence of ignoring cricketers based on nationality.
Franchises could be referred to the independent Cricket Regulator, although the ECB may also look to take separate action.
A total of 67 Pakistan players - 63 men and four women - have submitted themselves for the auction across March 11-12 in London, including Shaheen Shah Afridi, Shadab Khan, Haris Rauf and Naseem Shah.
Two Pakistan players - Mohammad Amir and Imad Wasim - featured in the 2025 edition of The Hundred, which was the last before private investment.
The four sides without IPL affiliation are London Spirit, Birmingham Phoenix, Trent Rockets and Welsh Fire.
There has effectively been a blanket ban on Pakistan players appearing in the IPL since 2009, while few have also appeared in other franchise leagues with Indian owners.
England white-captain Harry Brook, who will play for the Indian-owned Sunrisers this summer, was asked on Saturday about reports of Pakistani cricketers being excluded from The Hundred, which will run from July 21 to August 16.
Brook, currently leading England at the T20 World Cup in India and Sri Lanka, said: "Pakistan have been a great cricket nation for many years. There's some amazing cricketers and they bring some great crowds as well.
"It would be a shame to not see some of the Pakistan players in there and make this tournament and competition even better."
