May 24 (Reuters) - Citigroup has asked its 600 U.S. employees, who are eligible to work remotely, to return to office fulltime, it said on Friday as regulatory requirements make it hard for Wall Street banks to allow offsite work for roles such as trading.

Regulators had eased some of the stringent requirements to allow traders the flexibility of remote work during the pandemic.

But in the coming weeks, the primary watchdog for U.S. brokerage firms and exchange markets, the Financial Industry Regulatory Authority (FINRA), is set to bring back pre-pandemic rules to monitor workplaces.

"The majority of Citi employees will continue to work on a hybrid schedule, with at least three days per week in the office and up to two days remotely," the third-largest U.S. lender said in an email statement.

The private securities industry regulator had earlier this week pushed back against banks, saying its new rules provide member firms with greater flexibility — not less — to allow eligible registered persons to work from home, following the expiration of temporary COVID-19 relief.

Bloomberg News first reported Citi's move along with shifts in work policies at HSBC Holdings and Barclays .

London-based Barclays has mandated that its global investment banking staff must work in the office or travel to meet clients five days a week from June 1, the Bloomberg report said.

Meanwhile, HSBC is talking to almost half of its workforce in New York, around 530 employees, about shifting regulations, the report said, citing an interview with the bank's head of human resources for the U.S. and Americas.

The lender is trying to let as many people as possible retain the option of logging in from home if they would like to, the report said.

All three firms have had some of the most flexible post-pandemic working policies compared to their Wall Street counterparts. (Reporting by Manya Saini in Bengaluru; Editing by Tasim Zahid)