USCIS has announced that it has received more petitions for H-2B beneficiaries than there are visa available for the first half of fiscal year 2019. As a result, any petitions received after December 6 will be rejected if they request an employment start date before April 1, 2019.
Congress has made available 66,000 H-2B visas each year, with 33,000 reserved for each half of the fiscal year. Any unused visas from the first half of the fiscal year would, in theory, roll into those available for the second half.