Restrictions on Optioning/Recalling Players to/from the Minors

GENERAL RESTRICTIONS:

1. Beginning with the 2020 season, no more than 14 players (formerly no more than 16 players) on a club's MLB Reserve List (40-man roster) may be on Optional Assignment at any one time prior to September 1st, and no more than twelve players may be on Optional Assignment at any one time beginning on September 1st and extending through the conclusion of the MLB regular season.

2. No player may be optioned to a minor league club whose regular season (including post-season playoffs) has concluded.

3. No player may be optioned to the minors prior to the start of Spring Training.

4. Generally an injured player cannot be optioned to the minors. However, an injured player who did not accrue any MLB Service Time during the previous season, has not accrued at least three years of MLB Service Time, and was not selected in the previous Rule 5 Draft, can be optioned to the minors during a period of time beginning on the first day of Spring Training until the 15th day prior to the start of the next MLB regular season. 

CAN BE OPTIONED IF INJURED UNTIL 15TH DAY PRIOR TO 2021 MLB OPENING DAY (last updated 3-12-2020):
TBD   

6. A player who is optioned to the minors generally must remain on Optional Assignment for at least ten days (for a "position player") or 15 days (for a "pitcher or for a "two-way player"), and a "position-player" optioned to the minors during Spring Training generally must remain on Optional Assignment for the first ten days of the MLB regular season and a "pitcher" or a "two-way player" optioned to the minors during Spring Training generally must remain on Optional Assignment for the first 15 days of the MLB regular season. The only exceptions are if the player is traded or claimed off waivers, recalled as the "27th man" for a doubleheader (second game of the doubleheader only if two games were scheduled after a postponed or suspended game from the previous day), or is recalled to replace a player on the MLB Active List (26-man roster) who is traded, claimed off waivers, or placed on the MLB Injured List, Bereavement/Family Medical Emergency List, Paternity Leave List, or Restricted List (but only pursuant to a suspension or administrative leave resulting from a violation or possible violation of the joint MLB-MLBPA JDV policy or a suspension resulting from a violation of the joint MLB-MLBPA JDPTP policy).
NOTE: If a player is acquired in a trade and is optioned to the minors by his new club within 24 hours, the player can be recalled from the Optional Assignment at any time without restriction, but if a player on Optional Assignment to the minors is claimed off waivers and is then optioned to the minors by his new club, the ten-day limit (for "position players") or 15 day limit (for "pitchers" and for "two-way players") does apply. So as far as the ten-day ot 15-day limits are concerned, there is a distinction made between acquiring a player in a trade and claiming a player off waivers.   
CoViD-19 EXCEPTION: The minimum number of days a player generally must remain on Optional Assignment to the minors will be ten days for both position players and for pitchers in 2020.    

7. All players on Optional Assignment to the minors must be recalled no later than the day after the conclusion of the MLB regular season.

OTHER RESTRICTIONS:

8. A Rule 6 "Selected Player" cannot be optioned to the minors until restrictions have been removed.

RULE 6 SELECTED PLAYERS WITH MINOR LEAGUE OPTIONS REMAINING (updated 12-12-2019):
Trevor Megill, RHP

9. Beginning on the day after the conclusion of the MLB regular season, a Rule 6 "Draft-Excluded Player" cannot be optioned to the minors any earlier than 20 days prior to MLB Opening Day.
NOTE: An injured player with Draft Excluded Status who otherwise would be eligible to be optioned up until the 15th day prior to MLB Opening Day can be optioned only during a five-day window starting on the 20th day prior to the start of the MLB regular season up until the 15th day prior to the start of the MLB regular season.

DRAFT-EXCLUDED PLAYER WITH MINOR LEAGUE OPTIONS REMAINING (last updated 3-12-2020):
NONE AT THIS TIME  

10. Per Article XIX-A of the CBA, any player on an MLB 40-man roster who has accrued at least five years of MLB Service Time (as well as an international player with Article XIX-A contractual rights) has the right to refuse an Optional Assignment to the minors, or the player can elect to be a free-agent immediately upon being optioned (he has two days to decide).

If a player eligible to elect free-agency is optioned and elects to be a free-agent immediately, his contract is terminated and he receives no termination pay.

If a player with Article XIX-A rights refuses an Optional Assignment but does not elect free-agency, the club must either retain the player on the club's MLB Reserve List (40-man roster) AND Active List (25-man roster), trade the player, or give the player his Outright Release.

A player with Article XIX-A rights can waive his right to refuse an Optional Assignment in advance, but the waiver cannot be signed more than ten days prior to MLB Opening Day, the player has the right to designate in advance which minor league team to which he can be assigned, and the waiver automatically expires if the player is not optioned to the minors within 45 days or by the 45th day of the MLB regular season (whichever is later).

CUBS ARTICLE XIX-A PLAYERS WITH MINOR LEAGUE OPTIONS REMAINING (last updated 1-29-2020): 
Yu Darvish, RHP
Daniel Descalso, INF 
Kyle Hendricks, RHP
Jason Heyward, OF
Craig Kimbrel, RHP
Jon Lester, LHP
Jose Quintana, LHP 
Anthony Rizzo, 1B
Steven Souza Jr, OF