Generally, tribes as employers are responsible for the payment of federal employment taxes on wages paid to their employees. Federal employment taxes include FICA, FUTA (which is now optional; see Announcement 2001-16, 2001-8 I.R.B. 715), and federal income tax withholding.
NOTE: Employers are required to pay the employer's share of FICA tax on wages paid to employees. Employers are also responsible to withhold the employee's share of FICA, and federal income tax from the employee's wages.