DENVER -- The Regional Transportation District reached a tentative agreement Wednesday with unionized bus drivers, train operators and mechanics that includes a cash bonus for the workers, RTD said.

The executive board of the 1,750-member Amalgamated Transit Union tentatively agreed to the contract and will recommend it to their membership, which will vote on the contract on Sunday. Union officials said a strike would occur Monday if workers reject the deal. By law, the union would have to notify RTD 72 hours before going on strike and on Wednesday workers gave formal notice to RTD and the Colorado Division of Labor and Employment.

"It's basically the same offer we had previously, but we were able to also put in a signing bonus of $250 and agreed in years two and three to split any potential increases in health cares," said RTD spokesman Scott Reed.

The offer scraps an additional week of vacation that RTD had offered new employees in favor of a $250 cash bonus for all employees, Reed said.

The initial pay offer remains the same, with raises totaling about $1.80 per hour over the three-year deal.

The two sides have been at odds over wages and benefits in a contract to replace the one that expired Feb. 28. Negotiations began nearly two months ago.

Union members overwhelmingly rejected RTD's previous offer on Sunday.

"We're very pleased that we were able to come to this agreement, which is a very substantial and fair contract offer that we believe will be handily ratified by the union membership," Reed said.

Union leaders had objected to raises that RTD salaried workers got while workers' pay was frozen under a 2003 contract agreement.

The union said some executives got up to 50 percent increases.

"While the workers were trying to get along on the same salary, the same wage for three years, RTD was passing out bonuses and raises to executives like good cookies," union spokesman Dave Minshall said last week.

Reed said senior managers got raises averaging 2.5 percent last year to put them on even footing with industry peers. He said one manager received a 47 percent pay hike.

RTD's last strike was a walkout of about a month in 1982, Reed said.

If a strike does occur, all light rail lines in the metro area would be shut down. Some buses would run, but it's not exactly clear which routes would still be in operation.

"The workers have gone without a pay increase for three years. The workers will decide whether the deal is good enough for their families," said Minshall.

RTD serves the eight-county Denver area, which has more than 2.5 million residents. Last year, the system's buses and light-rail trains recorded 86.2 million passenger boardings.