Workers at the Pribbenow mine in northern Colombia, owned by U.S.-based Drummond, plan to end their strike on Wednesday after the expected signing of a new two-year contract Tuesday night, a union official said.

"We plan to sign the contract tonight and lift the strike tomorrow," union negotiator Sergio Becerra told Reuters.

The new accord will include a 9.1 percent pay increase for the first year of the deal and a raise of 1.75 percent plus Colombia's inflation rate for the second half of the contract, Becerra said.

A preliminary deal was agreed to earlier on Tuesday, he said. It includes a 2 million peso ($1,109) bonus to be paid to each of the open pit mine's 3,500 workers within 30 days of the signing of the contract, Becerra added.

Pribbenow produces about 2 million tonnes of coal per month, according to Drummond, a family run business based in Birmingham, Alabama.

The work stoppage began on July 17 after contract talks broke down in part over miners' demands for higher pay.