One of Tunisia's main political parties, the Constitutional Free Party, said on Sunday it would not recognise any agreement that Tunis makes with international lenders in exchange for unpopular reforms, the latest threat to a possible deal with the International Monetary Fund.

The director of the Middle East at the IMF, Jihad Azour, will visit Tunisia on Monday and meet President Kais Saied, in an indication that official negotiations could start soon over a rescue package.

Tunisia, which faces a financial crisis, is seeking a deal on a $4 billion loan from the IMF in return for an unpopular reform package to shore up its struggling public finances.

The government reform package included a wage freeze and cuts in food and energy subsidies.

The Constitutional Free Party, which polls say would win by a large margin over rivals in any parliamentary elections, joined UGTT union in rejecting economic reforms demanded by the IMF.

The powerful UGTT union, with one million members, went on strike on Thursday and brought much of Tunisia to a standstill, over the government's economic reform plans, increasing pressure on President Kais Saied.

"We will not recognise any financial commitments or loans between the government and international donor institutions," the party said in a statement.

The party is led by Abir Moussi, a supporter of autocrat? ?President Zine El Abidine Ben Ali, who was overthrown by mass protests in the 2011 revolution.

After a decade of the revolution that brought democracy, Moussi's party has become a main player in Tunisia as popular frustration grows with economic stagnation.

On Saturday, thousands of the party's supporters protested against President Saied.