Transport unions have warned of a looming strike in the bus sector after two months of wage negotiations failed to result in an agreement.

A four-day mediation over a week ago also failed to get to an agreement between Satawu, Numsa and three other unions in the South African Road Passenger Bargaining Council.

Satawu spokesperson Zanele Sabela said the strike seems inevitable next month.

"Satawu, Numsa, Towu, Tawusa and Taswu were given a certificate of non-resolution after the four-day mediation they took part in with employer associations COBEA and SABEA failed to produce a wage agreement.

"The mediation process was overseen by commissioner Tariq Jamodien and it failed to reach a settlement," Sabela said.

She said parties "will now observe a 30-day cooling-off period".

Numsa spokesperson Phakamile Hlubi-Majola said although it already has the strike certification, going that route remains its last resort.

"For us, we still hope to reach a resolution because strikes are difficult for everyone and they always remain a last resort," she said.

Hlubi-Majola said even though it has had three rounds of negotiations, including two mediations failing, it hoped employers would return with something on the table worth taking back to workers.

The unions are now pinning their hopes on the last round of mediation set for March 30 to April 1.

Wage negotiations in the bus sector started in January and were followed by several unsuccessful mediations in late February and now in March.

Sabela said unions initially had an 18-item demand list.

"Over the last three rounds, they withdrew nine items in an effort to move towards an agreement.

"Employers, on the other hand, remained rigid, only giving two improvements, namely fixed-term contract workers becoming eligible for benefits after six months' work and the scope of family responsibility extending to include illness of a spouse, not just death," she said.

The unions are seeking a one-year agreement while employers want a three-year settlement. Sabela said employers insisted on different wage increments for different categories of workers.

Labour has proposed an 8.5% and 7.5% increment for the two categories of workers respectively while employers are offering 6% for year one, 5.5% for year two and 5.5% for year three for one category and 4.5% increase for each of the three years for the other category.