The boards of both the companies have passed resolutions to hike the limit of foreign investment to up to 74 per cent, RBI said.
Earlier, foreign investment in Federal Bank was 49 per cent and that in Sintex Plastics was 24 per cent.
"The increase is subject to regulation 5(2) and 5 (2A) of Foreign Exchange Management (Transfer or issue of security by a person resident outside India) Regulations, 2000...As amended from time to time, and the onus of compliance with the limits prescribed for the company is on the company," RBI said.
RBI monitors ceilings on FII/NRI/PIO investments in Indian companies on a daily basis.
It has fixed the cut-off points two percentage points lower than the actual ceiling.