Queen Elizabeth II, Britain's longest reigning monarch, has died in Balmoral at the age of 96 after a 70-year reign.
The planned strike of postal workers on Friday, September 9, and the strikes of RMT railway workers on September 15 and 17 have been suspended.
Aslef, the union of train drivers, has also postponed the strike scheduled for September 15.
A spokesman for the Rail Delivery Group, which represents train operators, said he welcomed the RMT's decision to call off the strike next week during "national mourning".
"The entire railway family is united in expressing condolences to the royal family," a spokesman said.
Network Rail has confirmed that trains will operate as normal next week.
