5 U.S.C. § 3304a

1. (a)An individual serving in a position in the competitive service under an indefinite appointment or a temporary appointment pending establishment of a register (other than an individual serving under an overseas limited appointment, or in a position classified above GS–15 pursuant to section 5108) acquires competitive status and is entitled to have his appointment converted to a career appointment, without condition, when—
   1. (1)he completes, without break in service of more than 30 days, a total of at least 3 years of service in such a position;
   2. (2)he passes a suitable noncompetitive examination;
   3. (3)the appointing authority (A) recommends to the Office of Personnel Management that the appointment of the individual be converted to a career appointment and (B) certifies to the Office that the work performance of the individual for the past 12 months has been satisfactory; and
   4. (4)he meets Office qualification requirements for the position and is otherwise eligible for career appointment.
2. (b)The employing agency shall terminate the appointment of an individual serving in a position in the competitive service under an indefinite or temporary appointment described in subsection (a) of this section, not later than 90 days after he has completed the 3-year period referred to in subsection (a)(1) of this section, if, prior to the close of such 90-day period, such individual has not met the requirements and conditions of subparagraphs (2) to (4), inclusive, of subsection (a) of this section.
3. (c)In computing years of service under subsection (a)(1) of this section for an individual who leaves a position in the competitive service to enter the armed forces and is reemployed in such a position within 120 days after separation under honorable conditions, the period from the date he leaves his position to the date he is reemployed is included.
4. (d)The Office of Personnel Management may prescribe regulations necessary for the administration of this section.