This is what is known as a [I]dynamic spread[/I], “dynamic” because it is subject to change, versus a “fixed” spread, which is not no matter the market context.
Not all brokers use them, but of those that do, you’ll see spreads widen on Sunday evening, Friday afternoon, and on specific pairs just before and during release of economic data that impacts either currency. Brokers do this to maintain a liquidity balance because there are either (in the case of Sundays/Fridays) fewer participants or a sudden burst in order flow (as in the case of news releases) where an atypically high number of market participants are entering and exiting the market at once.