Mexicans continue to head north in search of work, apparently hoping U.S. employers will ignore a new law banning them from hiring illegal aliens, authorities say.

"I think we're going to show them we're serious about enforcing employer sanctions," Border Patrol agent Jerry Hicks said Tuesday after authorities arrested 42 people stowed aboard a freight train.One of those arrested, Tomas Vega of San Luis Potosi, Mexico, said he got on the northbound railroad grain car without knowing what city he would reach.

"I came to find work wherever it (the train) stops," the 21-year-old undocumented alien said, adding he could not find a job in Mexico.

Vega and about 16 others, including a man carrying a crying 3-year-old boy, appeared stunned Tuesday as they climbed down a ladder from the grain car. Their trip was cut short 30 miles north of the Rio Grande.

The 42 aliens found scattered along the Houston-bound train are among the thousands of people officials say are continuing to flock to this country illegally every week.

Employer sanctions under the Immigration Reform and Control Act of 1986 go into full effect June 1.

Hicks, the deputy chief patrol agent with the Border Patrol's McAllen Sector, said the numbers have been increasing lately, and agents who stopped the train Tuesday had expected to find even more aliens in the train's 113 cars.

Immigration officials say lack of employment in Mexico is prompting the aliens to take their chances on whether employers will flout the new law.

A recent five-day sweep of trains netted more than 100 aliens per day, officials said, including a group suffering from dehydration in a sealed boxcar.

"The situation in Mexico is terrible, and people are caught in a situation where their country has nothing to offer them," said Telma Longoria, director of Catholic Social Services for the church's Brownsville Diocese.

She said the diocese is seeing more Central Americans than ever at its Casa Oscar Romero shelter east of Brownsville, which averages 150-200 aliens at any time.

With the weather warming up, immigration officials said they are checking the trains more often in order to prevent a repeat of the tragedy in Sierra Blanca last summer, when 18 aliens suffocated in a sealed boxcar in the west Texas heat.

On hand to observe Tuesday morning's predawn train operation were Jim Olech, the Border Patrol chief in Washington, and Henry Oncken, the U.S. attorney for the Southern District of Texas.

The Border Patrol's McAllen sector reported 1,691 apprehensions of undocumented aliens during the first week of May, most of whom were not on trains. Last week, the sector reported 1,080 apprehensions, 204 involving people from countries other than Mexico, said Fred Rangel, a Border Patrol intelligence agent in McAllen.