I am getting an error while running this code - Incorrect syntax near the keyword 'IF'.

I need the output through function only with table return .

CREATE FUNCTION [dbo].[fnct_rpt_ActiveHC_WithoutGrp_tarun1]
 (
  @adid1 varchar(25),
  @number int
 )
 RETURNS TABLE
 AS
 RETURN
  IF  @adid1 in ( 'tachakr','BEULA','NI345519')
 BEGIN 
      SELECT * 
      FROM	OD_SAP.dbo.ty_rpt_ActiveHC_WithoutGrp a
JOIN	[BI_Control].[dbo].[tbl_BI_AccessMatrix_ADIDcc] b ON a.CostCode = b.cc
JOIN	[BI_Control].[dbo].[tbl_BI_AccessMatrixMaster] C ON b.ADID = c.ADID AND C.IsActive = 1
 END 
ELSE 
  BEGIN 
      SELECT
		EmployeeID, EmployeeName, DOB, Gender, DOJ, LevelCode, TEDRole, OrgRoleDesc AS OrgRole, Designation,
		Productive, Billable, Phase, TraineeType, BenchReason, ShiftCode, EmpLocation,
		BossID, BossName, OrgID, ProcessName AS OrgName, OrgLocation, CostCode, CompCode, GroupName,
		BUHead, Site, ForDate, ETL_DateTime
FROM	OD_SAP.dbo.ty_rpt_ActiveHC_WithoutGrp a
JOIN	[BI_Control].[dbo].[tbl_BI_AccessMatrix_ADIDcc] b ON a.CostCode = b.cc
JOIN	[BI_Control].[dbo].[tbl_BI_AccessMatrixMaster] C ON b.ADID = c.ADID AND C.IsActive = 1
where	b.ADID = @adid1 AND b.ReportID = @number

  END