Teams in The Hundred face having to re-negotiate with some of their star names depending on whether or not they are given an England central contract.
Each of the eight men's teams chose a player with an England Test contract for the 2020 season, which was postponed because of coronavirus.
However, if a team now has more than one player with a Test contract in 2021, they must choose which to keep.
The others will go into an 'England pot' and could be re-allocated.
An example of this would be Southern Brave, who would have had Jofra Archer and Ollie Pope for the 2020 season, both of whom can expect England contracts for the coming year.
Brave would have to choose which player to keep, with the other then becoming available to teams who do not have a contracted player.
Conversely, Welsh Fire's contracted player was Jonny Bairstow, who could lose his England deal. Fire can still negotiate to keep Bairstow as part of their remaining roster but, if no agreement is made, he would become a free agent and enter the draft.
All teams will have at least one England contracted player, but no more than two.
The contracted players can also opt of playing in The Hundred, like James Anderson and Stuart Broad did in 2020.
After England players are allocated, teams can negotiate with the rest of their squads and can potentially keep all of them, depending on availability and price band.
Contracts in 2021 will be across seven price bands between £100,000 and £24,000, down from £125,000 and £30,000 in 2020.
Kolpak players will not be permitted next year, so they would potentially have to become overseas players, of which each squad is allowed a maximum of three.
Once player retentions are agreed, there will be a draft to fill remaining slots in squads in early 2021.
In the women's Hundred, all players can roll over their 2020 contracts to 2021, with any not choosing to do so then free to be selected in an open-market system.