Congress has declined to renew the higher annual cap on H1-B visas, rolling them back to 65,000 for the fiscal year starting today from 195,000 in 2000. H1-B's allow "employers to hire foreign workers with special skills they can't find among American job applicants," typically for high-tech jobs. But H1-B's are also used for visiting researchers at industrial research labs and some university positions. When the limit is reached, the government will no longer issue more visas until the start of the next fiscal year.
At NEC, we had postdocs who had to delay their start date until October for this reason, including in some cases those who wanted to start at the beginning of summer. With the limit dramatically decreased, if the job market starts perking up, we could hit the limit much earlier. This could make a real dent in international cooperation in science.