Estrada was featured on Automotive News' list of the 100 Leading Women in the North American Auto Industry in 2010 and 2015.
The departures mean at least two of the Detroit 3 UAW vice presidents will be new to their roles when labor contract negotiations begin next year.
Estrada and Dittes led bargaining for their respective companies during the 2019 labor contract negotiations that prompted a 40-day strike by GM's hourly workers.
Under a new direct-election voting system, UAW leaders will be nominated at the UAW Constitutional Convention in late July. Members will then vote for vice presidents of the Stellantis, GM and Ford departments.
In December, UAW members voted for the direct-election system for union leaders, rather than the delegate system that many considered an enabler for corruption among the top ranks after a wide-ranging investigation sent two former union presidents and 13 others to prison.
A federal judge approved the members' vote in February and ordered the union to implement the new voting system by June 30.