The school district that runs the nation's largest merit pay program gave oversized bonuses to nearly 100 teachers and is asking them to give it back. The president of Houston's largest teachers' union is telling members not to return the overpayments, which range from $62.50 to $2,790.

A total of almost $75,000 was overpaid because a computer program mistakenly calculated the bonuses of part-time personnel as if they were full-time employees, according to the Houston Independent School District. Less than 1 percent of teachers were affected, the district said.

Gayle Fallon, president of the Houston Federation of Teachers, said the district can't force the 99 teachers to sign forms authorizing it to deduct the money from their paychecks, and promised legal action if it attempts to do so.

"If it's the district's error, then the district should bear the loss," she said.

District spokesman Terry Abbott, however, said the money must be repaid.

The union opposes the merit system unanimously approved by the school board last year. The district doled out $14 million to almost 8,000 teachers two months ago, but distributed another $1 million after officials realized several hundred teachers had been overlooked.

Salaries for full-time teachers in the district range from about $40,000 to nearly $68,000.