OAKLAND — BART said Monday that it would need to raise fares 18 percent over the next three years if it gave in to union demands for pay raises exceeding 20 percent over three years.

“We would like to avoid that,” BART spokesman Rick Rice said of steep fare hikes to cover pay increases.

Meanwhile, BART contract talks continued Monday in Oakland in an effort to avoid a second potential strike that union leaders have said they may call Aug. 5 if no contract agreement is reached by then. A four-day strike was held earlier this month.

BART and union negotiators are expected Tuesday to tackle pay and medical and pension benefits, which have been big sticking points in negotiations.

Before state mediators earlier this month issued a gag order on details of the latest contract proposals, BART’s two major unions had asked for a 20.1 percent pay increase over three years.

BART had offered a four-year increase of 5 to 8 percent, depending on whether certain economic conditions were met.

Rice said Monday that the demand for a 20.1 percent pay increase would translate into a an 18 percent fare increase over three years — on top of inflation-related increases already approved by the board to help pay for new rail cars and other items.

Antonette Bryant, president of the union for train operators and station agents, said she is skeptical of BART’s calculations connecting pay proposals to fare increases. “I have a little difficulty with those numbers,” she wrote in a text message.

Meanwhile at a national transportation conference in San Francisco, chanting BART workers interrupted a speech by BART General Manager Grace Crunican and criticized her for not participating directly in contract talks.

BART has said Crunican’s personal appearance at talks is not necessary because she is kept up to date on the negotiations.

Contact Denis Cuff at 925-943-8267. Follow him at Twitter.com/deniscuff.