PETALUMA -- Calix, Inc. (NYSE: CALX) on Wednesday warned that its forthcoming fourth-quarter revenue at this point looks to be 3.6 percent to 8 percent lower than earlier anticipated, with pro forma earnings one-third to half of expectations, citing atypically slower year-end purchases from key broadband network operators.

For the fourth quarter, which ended Dec. 31, preliminarily estimates of revenue are $93.5 million to $94.5 million and of non-GAAP earnings per share of 2 cents to 4 cents, according to a company statement after the close of trading.

That's down from estimates of $97 million to $103 million and 3 cents to 8 cents per share on Oct. 29. Analysts had been expecting $100.5 million in sales and earnings of 7 cents a share for the final quarter of 2013. Calix reported $91.4 million in revenue and 6 cents a share in pro forma earnings in the fourth quarter a year before.

"The revised estimates for the fourth quarter reflect a greater-than-anticipated decline in traditional year-end 'budget flush' customer spending patterns than the company historically has experienced," the announcement said.

The price of Calix stock dipped a half-percentage-point, or 5 cents a share, to $9.24 in regular trading Monday. The price had dropped 8.55 percent, or 79 cents a share, to $8.45 in after-hours trading a half-hour after the closing bell.

The alert on lower-than-expected fourth-quarter revenue comes after another Petaluma telecommunications systems developer, Cyan, on Monday said its sales for that period appear to have dropped more than one-third, attributing the drop to an 88 percent pullback in ordering by its largest customer from the third quarter. Cyan's stock price slipped $1.79 a share, or by one-third, during trading Tuesday and Wednesday to $3.50 a share.

Calix plans to discuss its fourth-quarter on a conference call at 1:30 p.m. Feb. 11.