Starbucks' new CEO Brian Niccol has his work cut out for him.

Tasked with reassuring investors that the company's coffee shops are still hugely popular in the U.S., Niccol also has to contend with baristas and hardcore Starbucks customers who say they want plenty of changes.

Baristas complain about what they say are chronic understaffing and poor pay and benefits, and their inability to easily ban aggressive customers from Starbucks stores. Zealous customers want consistently good coffee.

Shares of the company were down about 5% in premarket trading.

On Tuesday, after Starbucks reported a 6% fall in fourth-quarter same-store sales in the U.S. and pulled its earnings guidance for the coming fiscal year, Niccol said baristas need to be supported to provide "exceptional service" to customers.

"To succeed, we need to address staffing in our stores, remove bottlenecks, and simplify things for our baristas," he said in a video statement.

Liv Ryan, a barista and union organizer at a Starbucks in Long Island, New York, said that Niccol should put "an end to short staffing."

She said baristas have long had gripes about the lack of guidance from Starbucks on how to contend with bad-tempered customers.

"I have been told countless times that part of our job is 'just taking rude customers,'" Ryan said. "But there's no clear line between 'rude' and 'hostile' and even then I shouldn't have to put up with anyone being rude to me at my job."

Several other baristas who are part of, or who aim to be part of, the new Starbucks Workers United union, want to see Starbucks complete the contract bargaining process with workers. "All I’m looking for is a collective bargaining agreement by the end of the year," said Parker Davis, a union organizer at a Starbucks in San Antonio.

Niccol in the video said he would share more details about possible changes on the company's earnings call on Oct. 30, after Starbucks releases earnings for its fourth quarter and the year as a whole.

"We suspect multiple avenues of attack (by Niccol) are likely, including increasing labor hours at stores and reducing the frequency of limited-time promotions," said William Blair analyst Sharon Zackfia.

As for the coffee itself, it's overroasted, according to a zealous Starbucks customer whose legal name is Winter.

Winter, who has visited more than 19,000 Starbucks locations across the world in a quest to visit every corporate-owned location, said he still enjoys the atmosphere at the Starbucks – at least when it isn’t the morning rush – but these days, he’s found the coffee wanting.

He used to like it back in 1997, he says, but Starbucks has since made its menu far more complex with specialty coffee orders. "And getting a fancy drink isn’t going to make me enjoy it any more."