SMark Zuckerberg's college-spawned startup is supposed to hire its 1,000th employee sometime this year. I don't think that's going to happen. If Zuckerberg isn't talking about layoffs behind closed doors, one of his executives must be brave enough to bring it up. I don't think the company is going to issue pink slips. But I do think its headlong growth in employees will come crashing to a halt before the end of the year.Here's some back of the envelope math on Facebook's burn rate. Figure the company's operating expenses are divided roughly half in labor, half in operations like running its servers. Count $100,000 in salary per employee, and double that in benefits and other overhead; double that again to account for the company's non-labor costs. You end up with an annual cost structure of $400 million. Facebook's revenues for this year are projected to be $300 million to $350 million; if the company isn't already operating in the red, it's headed there fast. Microsoft's $240 million investment? Most of that is already gone towards buying servers — and it's not like Facebook can stop buying servers as usage of its site continues to boom. Publicly, Zuckerberg has talked about the company making growth its priority. But a $400 million a year ship can sink fast, especially if the advertising market faces a hard contraction and media buyers cut back on their more experimental ad buys. And none of Facebook's new ad formats have proven to be a breakout hit, as Google's AdWords was earlier this decade. That's why I think Facebook's braintrust is talking about whether they can afford to keep hiring — and whether they need to cull their existing ranks. Here's where Facebook COO Sheryl Sandberg, the law-and-order type Zuckerberg hired from Google, comes in. She's already made hiring considerably more bureaucratic, instituting new requirements straight out of the Googleplex, like a 3.5 GPA from a top school. Getting strict on recruiting is just the start. Facebookers should expect to see more rules, rules, rules. And even the slightest violation will prove cause for firing — especially for employees who are within weeks of vesting their first batch of stock options, which only come after a year on the job. Sandberg's very savvy about keeping up appearances. Google thrived in part because, in the darkest days of the dotcom crash, from 2001 through 2003, it was the only company hiring. Until it bought DoubleClick, Google had never done a layoff. That's part of Google's image, and I'm sure Sandberg wants it to be part of Facebook's image, too. So we won't hear about a Facebook hiring freeze. We certainly won't hear about layoffs. Whatever happens will be quiet: Candidates won't get called back about jobs they applied for. Managers will find their hiring requests tied up in bureaucracy. And employees will quietly box up their things and go. The sad thing is that those Facebookers will think they screwed up. They won't even have the saving grace of a layoff — the corporate kiss-off that says, "Hey, kid, chin up — it's not you, it's me." A layoff would be the honest thing. But it's the one cost-cutting move Facebook can't afford.