Workers at the stores addressed a letter to Starbucks CEO Kevin Johnson revealing their intent to unionize.
"We are organizing a union in Boston because we believe that this is the best way to contribute meaningfully to our partnership with the company," the letter stated.
"As partners and core contributors to the company's success, we deserve respect. This includes listening and responding to our communications."
Just last week, Strabucks workers in Buffalo, New York voted to unionize after the National Labor Relations Board rejected Starbucks' attempt to stop a vote count.
The serious push for unionization began in the summer after employees started bringing up understaffing, faulty equipment and underpayment despite record Starbucks sales of $29 billion in 2021 in the summer.
Starbucks announced in October that it would raise the pay of all hourly-pay employees to at least $15 an hour and an overall average of nearly $17 an hour by summer 2022 but the movement had already started to gather steam.
Earlier this month, Starbucks was upgraded to buy by analysts at MKM Partners due to a bullish view on the company's long-term prospects.
The firm estimated that Starbucks will invest about $1 billion into annual wages and benefits growth, which is causing a "short-term drag on fundamentals."