Getting error: Ambiguous column name 'ecode'

Question

Select top(20) sno,ecode,name,mobile_no,department,doj,ctc
from charbi..mst_emp_master(nolock)a
inner join charbi..new_emp_salary_master(nolock)b
on a.ecode=b.ecode 
where status='Y'
order by doj  desc




i m getting error as




Msg 209, Level 16, State 1, Line 1
Ambiguous column name 'ecode'.



pls let me know what im doing wrong.