The Republican-led Legislature approved the measure this year. Supporters say the requirement would prohibit abortions using telemedicine and protect a woman's health and safety by ensuring the prescribing physician is present.
Critics say the process is safe and that the legislation is a further effort to restrict access to abortion services in Missouri.
Nixon, a Democrat, can sign, veto or allow the new law to take effect without his signature. The governor was expected to announce his decision Friday. Nixon allowed abortion laws to take effect without his signature in 2010 and 2011.