Equatorial Guineans will vote on a referendum to the constitution Sunday that would limit the country's president to two seven-year terms.

Those opposing the measure say it provides additional authority to President Teodoro Obiang Nguema, who already wields influence over the legislative and judicial branches of the tiny west African country.

President Obiang's government says the new constitution will provide better oversight over the executive branch, improve human rights and the judicial system.

If approved, the changes would also create a vice presidency. Critics, including Human Rights Watch , say the new constitution would allow President Obiang to handpick the candidate.

The opposition says Mr. Obiang would likely choose his son to fill the vice presidential slot, putting him in position to succeed him.

Another change in the constitution removes the maximum age limit for a president. In the case of President Obiang,who is 69, he would not qualify to run after age 75. Mr. Obiang is Africa's longest serving president. He first gained gained power in 1979.

President Obiang's administration has struggled to shake off a reputation for corruption.

HRW says President Obiang's son is under investigation for corruption and money laundering in France, Spain, and the United States.