WHEN CONGRESS returns after the Easter recess, Immigration subcommittees in both houses will begin to mark up immigration reform legislation. The Simpson-Mazzoli bill was passed by the Senate last year but died in the final hours of the 97th Congress on the House floor. It is badly needed legislation that will, among other things, penalize employers who hire illegal aliens.

The governor of Texas knows what the influx of illegal aliens is doing to the economy of his state. Border towns already hard hit by the loss of Mexican trade because of the devaluation of the peso have also had to deal with an unchecked tide of workers coming across the border and competing for scarce jobs. In some counties in the lower Rio Grande Valley, unemployment is at 50 percent, and the strain on local governments charged with providing social services to a population that has increased at a rate five times the national average is great.

It is easy to understand why the immigrants continue to wade across the river to what they hope will be a better life. They come for jobs, as immigrants always have, and in better times there were always jobs to be had that citizens did not want. All that has changed. Across the country, people who never thought they would work for minimum wage are lining up for any kind of employment.

The leaders of the AFL-CIO understand what illegal competition is doing to American workers. They know that as long as employers bear no penalty for hiring illegal workers instead of Americans they will continue to do so, for those without papers are far less likely to organize, to ask for pay increases or to demand better working conditions.

Last month, at their annual meeting in Bal Harbour, Fla., the leaders of the labor organization issued a policy statement urging Congress to act on immigration reform legislation. Congress has a responsibility to act early on this plea. Moving the Simpson-Mazzoli bill to the floor this spring is a must.