Jennifer Aniston reportedly feels "exasperated" by Justin Theroux putting off their wedding.
The 44-year-old actress and her Wanderlust co-star announced their engagement in December 2012.
After a year of having a ring on her finger Jennifer is said to be keen to walk down the aisle as soon as possible. However, Justin is thought to be stalling the wedding and upsetting his fiancée in the process.
"Jen's told Justin she feels exasperated that he's dragging his feet over the wedding," a source told British magazine Closer. "She's given him an ultimatum to have set a date with her by the end of this year."
Justin is currently filming his new TV series The Leftovers in his hometown of New York City. While he works in the Big Apple Jennifer has remained in their Bel Air mansion, which she hopes will be their marital home.
During their time in different cities the couple's relationship is reportedly strained, especially since Justin is believed to want to stay put in New York.
"Jen renovated her home to entice Justin to LA but, after filming in New York - which is where he lived before meeting Jen - he's realised that's the place he wants to be," the insider added.
"Jen's told friends that postponing the wedding because of work on the house, coupled with the distance between her and Justin, has been pushing them apart."
To add to the tense atmosphere Justin is said to be spending a lot of time with his The Leftovers co-star Emily Meade. Although he has assured Jen their relationship is simply platonic the former Friends actress is thought to be worried.
"Justin's been spending time with Emily on and off set. He's reassured Jen there's nothing going on, but it's led to a few rows," an insider added. "Justin insists he wants to marry Jen, but she's been confiding in her pals her fears of bring in the New Year as a singleton. And that's not something she wants."