NEW YORK, Jan 21 (Reuters) - Citigroup (C.N) has told staff in the New York Tri-State area to start returning to the office from Feb. 7, while BNP Paribas (BNPP.PA) is targeting the same date for U.S. staff after recently postponing its return-to-office plans by nearly a month due to the Omicron variant. Wall Street firms were among the first to encourage staff to return to offices, but a winter wave of COVID-19 infections driven by Omicron has forced many to rethink their plans and review their vaccination policies in recent weeks. "With what happened with Omicron, we wanted to go back into a more conservative mode. So we only have people in the office if there"s a business critical need for them to be in," said Kevin Abraszek, head of HR change and transformation at BNP Paribas in New York. Citigroup, which sent staff at its New York metro area office home in mid-December as Omicron spread, has asked staff to prepare for a return to the office starting on Feb. 7, a person familiar with the matter told Reuters on Friday. In other locations, return-to-office plans are still on pause and the bank will continue to monitor the data, the same person said. Staff will be expected to be in the at least two days a week, as was its policy before the holidays. Citigroup said this month U.S. employees who had not been vaccinated against COVID by Jan. 14 would be placed on unpaid leave and fired at the end of the month unless they were granted an exemption and accommodation. BNP Paribas, which employs nearly 14,000 people in the United States, will expect U.S. employees to work at least one day a week in the office once they return, similar to its policy late last year before Omicron struck. A bank spokesperson said the return to office policy applied only for investment banking employees, not for employees of BNP Paribas" U.S. retail arm, Bank of the West. Abraszek said vaccination against COVID-19 was a requirement to be in the office, but the bank was allowing employees who have not been vaccinated to continue working from home. "I think we"re going to continue to look at that decision and that policy in the early part of this year," he said. The bank plans to bring capacity back up to 50% gradually once employees start to return, said Abraszek. "We were generally skewing around 25% to 30% late last year," he said. "We"ll probably reach that level and then our hope is that over the course of the spring, and certainly into the summer, that we will get closer to that 50%." Goldman Sachs Group Inc (GS.N) recently delayed its return-to-office date from Jan. 18 to Feb. 1.