Almost half of US employees aged in their mid-20s and 30s are unhappy at work and plan to change jobs this year, according to an Aon Hewitt survey.

The unhappiness among Millennials (those born after 1980) – or Generation Y – stems from a gulf in expectations between them and employers.

“Our research shows there is a clear disconnect between what Millennials expect and desire from employers and what their employers are actually offering,” Employee Research Leader Ray Baumruk said.

“This gap is negatively affecting the engagement and retention of this generation, and may be one of the primary reasons why Millennials will be looking for new opportunities.”

The survey of more than 2500 US employees in companies with at least 1000 staff shows 43% of Millennials intend to look for new jobs this year.

Pay and benefits are a problem area for 51% of these staff. Career prospects and opportunities are an issue for 39%, followed by performance recognition at 38%.

“The data show there is a significant opportunity for employers to offer a more unique and compelling work experience that will match what Millennials want, and in turn increase retention long term,” Aon Hewitt Communication Consulting Partner Pam Hein said.