Nov 4 (Reuters) - American Airlines Group Inc (AAL.O) delayed the rollout of a mandate that requires its U.S.-based employees to be vaccinated against the coronavirus until Jan. 4, Chief Executive Doug Parker said in a letter to employees on Thursday. This comes hours after the Biden administration moved forward the vaccination deadline for large U.S. companies from Dec. 8 to Jan. 4. read more Separately, Southwest Airlines (LUV.N) said it was reviewing the revised guidance from the administration. Biden had in September unveiled plans for the mandate, seeking to increase vaccination rates amid a dangerous surge in COVID-19 cases and get more people back to work. Reporting by Rhea Binoy and Sanjana Sitara in Bengaluru and David Sheperdson in Washington; Editing by Arun Koyyur Our Standards: The Thomson Reuters Trust Principles.