Lautenberg said the screeners, particularly at the country's biggest airports, are overworked, while some are understaffed and security lines are long.
"It's a strain on them and they just can't take it," Lautenberg said.
The TSA had no immediate comment on the Senate action, which came a day after the fifth anniversary of the 2001 hijacked plane attacks on New York and Washington. At that time, airport screeners were employees of private companies. Soon after, Congress created the TSA and made the hiring of screeners a federal government responsibility.
Sen. Ted Stevens, an Alaska Republican and chairman of the Senate Commerce Committee, said lifting the cap was unnecessary because TSA employs about 41,000 screeners -- about 4,000 below the current limit.
Stevens said turnover among screeners is high and the government could not fill many of the jobs because of the long hours, difficult work, and a security vetting process that takes months.
"The solution is to find some way to make the job more attractive, may pay them more," Stevens said. "Lifting the cap is not the answer."
He argued that adding more screeners would take money away from efforts to adopt and pay for bomb detection and other technology, which some government officials believe could help to significantly reduce screener staff.
The House of Representatives did not include the screener provision in its port security bill and the matter will have to be decided in House-Senate negotiations to reconcile both versions of the bill.