The RWN (Rating Watch Negative) reflects the unexpected eruption in political risk and uncertain political and economic outcomes. Social unrest began in mid-December and recently spread to the capital, Tunis, Fitch said in a statement.
Fitch's rating, two notches above junk status, is equal to the ratings given by Standard & Poor's (BBB) and Moody's Investors Service (Baa2).
Authorities declared a state of emergency and an overnight curfew on Friday. Tunisian President Zine al-Abedine Ben Ali fired his government and called an early parliamentary election. The moves come after a month of violent protests against unemployment, repression and corruption.
Ben Ali, in power since 1987, is making increasingly frantic efforts to quell the worst unrest in his more than two decades of power.
The calling of early elections and a promised opening-up of the political system introduce further uncertainty, Fitch said, adding that it expects to make a decision on the rating within six months.
Renewed disorder, with negative consequences for the economy, would lead to a downgrade, the firm added.
Fitch noted that the government faces external bond repayments equivalent to $750 million in April and September, 2011. Sovereign foreign currency deposits held at the central bank are $1.5 billion, providing some short-term financing flexibility.
On Friday, Tunisian military units surrounded the international airport on the outskirts of Tunis, the capital, an airport official told Reuters by telephone.
Ben Ali said in a televised address on Thursday he would not seek a sixth term as expected in 2014.
While Tunisia's problems are shared by other countries in the region, the latest unrest was sparked when police prevented an unemployed graduate from selling fruit without a license. He set fire to himself and died shortly afterward of his burns.